Fix errors in the documentation for StkMapRecord

[khordadi]

Summary

The patch is straightforward and the reasons for the changes are obvious.

1. In llvm/lib/CodeGen/StackMaps.cpp, the comments above StackMaps::emitCallsiteEntries doesn't reflect the actual implementation of the StackMaps::emitCallsiteEntries.
2. In llvm/docs/StackMaps.rst, a { is missing.

llvm/docs/StackMaps.rst

Location[NumLocations] {
       uint16 : Location Size
       uint16 : Dwarf RegNum
       uint16 : Reserved (expected to be 0)
       int32  : Offset or SmallConstant
     }
     uint32 : Padding (only if required to align to 8 byte)
     uint16 : Padding
     uint16 : NumLiveOuts
-    LiveOuts[NumLiveOuts]
+    LiveOuts[NumLiveOuts] {
       uint16 : Dwarf RegNum
       uint8  : Reserved
       uint8  : Size in Bytes
     }
     uint32 : Padding (only if required to align to 8 byte)
   }
 
 The first byte of each location encodes a type that indicates how to

llvm/lib/CodeGen/StackMaps.cpp

 ///
 /// StkMapRecord[NumRecords] {
 ///   uint64 : PatchPoint ID
 ///   uint32 : Instruction Offset
 ///   uint16 : Reserved (record flags)
 ///   uint16 : NumLocations
 ///   Location[NumLocations] {
 ///     uint8  : Register | Direct | Indirect | Constant | ConstantIndex
-///     uint8  : Size in Bytes
+///     uint8  : Reserved (expected to be 0)
+///     uint16 : Location Size
 ///     uint16 : Dwarf RegNum
-///     int32  : Offset
+///     uint16 : Reserved (expected to be 0)
+///     int32  : Offset or SmallConstant
 ///   }
+///   uint32 : Padding (only if required to align to 8 byte)
 ///   uint16 : Padding
 ///   uint16 : NumLiveOuts
 ///   LiveOuts[NumLiveOuts] {
 ///     uint16 : Dwarf RegNum
 ///     uint8  : Reserved
 ///     uint8  : Size in Bytes
 ///   }
 ///   uint32 : Padding (only if required to align to 8 byte)