[AMDGPU] Update relocation record description.

[t-tye]

Summary

Document which relocation records are static and dynamic.

[kzhuravl]

LGTM

llvm/trunk/docs/AMDGPUUsage.rst

The following relocation types are supported:
 
   .. table:: AMDGPU ELF Relocation Records
      :name: amdgpu-elf-relocation-records-table
 
      ========================== ======= =====  ==========  ==============================
      Relocation Type            Kind    Value  Field       Calculation
      ========================== ======= =====  ==========  ==============================
      ``R_AMDGPU_NONE``                  0      *none*      *none*
-     ``R_AMDGPU_ABS32_LO``      Dynamic 1      ``word32``  (S + A) & 0xFFFFFFFF
-     ``R_AMDGPU_ABS32_HI``      Dynamic 2      ``word32``  (S + A) >> 32
-     ``R_AMDGPU_ABS64``         Dynamic 3      ``word64``  S + A
+     ``R_AMDGPU_ABS32_LO``      Static, 1      ``word32``  (S + A) & 0xFFFFFFFF
+                                Dynamic
+     ``R_AMDGPU_ABS32_HI``      Static, 2      ``word32``  (S + A) >> 32
+                                Dynamic
+     ``R_AMDGPU_ABS64``         Static, 3      ``word64``  S + A
+                                Dynamic 
      ``R_AMDGPU_REL32``         Static  4      ``word32``  S + A - P
      ``R_AMDGPU_REL64``         Static  5      ``word64``  S + A - P
-     ``R_AMDGPU_ABS32``         Static  6      ``word32``  S + A
+     ``R_AMDGPU_ABS32``         Static, 6      ``word32``  S + A
+                                Dynamic
      ``R_AMDGPU_GOTPCREL``      Static  7      ``word32``  G + GOT + A - P
      ``R_AMDGPU_GOTPCREL32_LO`` Static  8      ``word32``  (G + GOT + A - P) & 0xFFFFFFFF
      ``R_AMDGPU_GOTPCREL32_HI`` Static  9      ``word32``  (G + GOT + A - P) >> 32
      ``R_AMDGPU_REL32_LO``      Static  10     ``word32``  (S + A - P) & 0xFFFFFFFF
      ``R_AMDGPU_REL32_HI``      Static  11     ``word32``  (S + A - P) >> 32
      *reserved*                         12
      ``R_AMDGPU_RELATIVE64``    Dynamic 13     ``word64``  B + A
      ========================== ======= =====  ==========  ==============================
 
+``R_AMDGPU_ABS32_LO`` and ``R_AMDGPU_ABS32_HI`` are only supported by
+the ``mesa3d`` OS, which does not support ``R_AMDGPU_ABS64``.
+
+There is no current OS loader support for 32 bit programs and so
+``R_AMDGPU_ABS32`` is not used.
+     
 .. _amdgpu-dwarf:
 
 DWARF
 -----
 
 Standard DWARF [DWARF]_ Version 5 sections can be generated. These contain
 information that maps the code object executable code and data to the source
 language constructs. It can be used by tools such as debuggers and profilers.