[OPENMP, NVPTX] Support several images in the executable.

[ABataev]

Summary

Currently Cuda plugin supports loading of the single image, though we
may have the executable with the several images, if it has target
regions inside of the dynamically loaded library. Patch allows to load
multiple images.

[grokos]

Looks good. Do you think we should do the same for the generic-elf-64 plugin?

[ABataev]

In D49036#1156092, @grokos wrote:

Looks good. Do you think we should do the same for the generic-elf-64 plugin?

If it has the same problem then definitely yes.

libomptarget/plugins/cuda/src/rtl.cpp

 };
 
 /// List that contains all the kernels.
 /// FIXME: we may need this to be per device and per library.
 std::list<KernelTy> KernelsList;
 
 /// Class containing all the device information.
 class RTLDeviceInfoTy {
-  std::vector<FuncOrGblEntryTy> FuncGblEntries;
+  std::vector<std::list<FuncOrGblEntryTy>> FuncGblEntries;
 
 public:
   int NumberOfDevices;
   std::vector<CUmodule> Modules;
   std::vector<CUcontext> Contexts;
 
   // Device properties
   std::vector<int> ThreadsPerBlock;
public:
   static const int HardThreadLimit = 1024;
   static const int DefaultNumTeams = 128;
   static const int DefaultNumThreads = 128;
 
   // Record entry point associated with device
   void addOffloadEntry(int32_t device_id, __tgt_offload_entry entry) {
     assert(device_id < (int32_t)FuncGblEntries.size() &&
            "Unexpected device id!");
-    FuncOrGblEntryTy &E = FuncGblEntries[device_id];
+    FuncOrGblEntryTy &E = FuncGblEntries[device_id].back();
 
     E.Entries.push_back(entry);
   }
 
   // Return true if the entry is associated with device
   bool findOffloadEntry(int32_t device_id, void *addr) {
     assert(device_id < (int32_t)FuncGblEntries.size() &&
            "Unexpected device id!");
-    FuncOrGblEntryTy &E = FuncGblEntries[device_id];
+    FuncOrGblEntryTy &E = FuncGblEntries[device_id].back();
 
     for (auto &it : E.Entries) {
       if (it.addr == addr)
         return true;
     }
 
     return false;
   }
 
   // Return the pointer to the target entries table
   __tgt_target_table *getOffloadEntriesTable(int32_t device_id) {
     assert(device_id < (int32_t)FuncGblEntries.size() &&
            "Unexpected device id!");
-    FuncOrGblEntryTy &E = FuncGblEntries[device_id];
+    FuncOrGblEntryTy &E = FuncGblEntries[device_id].back();
 
     int32_t size = E.Entries.size();
 
     // Table is empty
     if (!size)
       return 0;
 
     __tgt_offload_entry *begin = &E.Entries[0];
     __tgt_offload_entry *end = &E.Entries[size - 1];
 
     // Update table info according to the entries and return the pointer
     E.Table.EntriesBegin = begin;
     E.Table.EntriesEnd = ++end;
 
     return &E.Table;
   }
 
   // Clear entries table for a device
   void clearOffloadEntriesTable(int32_t device_id) {
     assert(device_id < (int32_t)FuncGblEntries.size() &&
            "Unexpected device id!");
-    FuncOrGblEntryTy &E = FuncGblEntries[device_id];
+    FuncGblEntries[device_id].emplace_back();
+    FuncOrGblEntryTy &E = FuncGblEntries[device_id].back();
     E.Entries.clear();
     E.Table.EntriesBegin = E.Table.EntriesEnd = 0;
   }
 
   RTLDeviceInfoTy() {
 #ifdef OMPTARGET_DEBUG
     if (char *envStr = getenv("LIBOMPTARGET_DEBUG")) {
       DebugLevel = std::stoi(envStr);