[AMDGPU] Stop combining arbitrary offsets into PAL relocs (#80034)

PAL uses ELF REL (not RELA) relocations which can only store a 32-bit
addend in the instruction, even for reloc types like R_AMDGPU_ABS32_HI
which require the upper 32 bits of a 64-bit address calculation to be
correct. This means that it is not safe to fold an arbitrary offset into
a GlobalAddressSDNode, so stop doing that.

In practice this is mostly a problem for small negative offsets which do
not work as expected because PAL treats the 32-bit addend as unsigned.