This is no longer supported as of gfx9. Fixes#52903
This commit also includes some refactoring of sendmsg operand parsing:
- Use CustomOperand for sendmsg operations, this allows them to be
conditionally available based on a STI check (and automatically in
sync with SIDefines.h).
- Move CustomOperand table lookups from AMDGPUBaseInfo to
AMDGPUAsmUtils. This cleans up an awkward interface where
AMDGPUAsmUtils defined a table/size as globals that AMDGPUBaseInfo
had to loop over.
- Clean up a few of the operand lookup functions while moving them.
dcc7ef3ce8