[llvm] [AMDGPU] Only src0 and mandatory literals can use literal64 (PR #196456)

[Stanislav Mekhanoshin via llvm-commits]

rampitec wrote:

In general the basic reason here: src2 cannot use lit64 ever, because having src2 mean VOP3 and we exceed 3 dword encoding limit. VOP2 only allow 8 bit for src1, meaning literals are not allowed at all. Which left us with src0 allowed for VOP1 and VOP2.

https://github.com/llvm/llvm-project/pull/196456