[RISCV] Clear isCodeGenOnly flag on VMSGE(U) pseudo instructions. Remove...

[RISCV] Clear isCodeGenOnly flag on VMSGE(U) pseudo instructions. Remove InstAliases that duplicate the asm strings in the pseudos.

The Pseudo class sets isCodeGenOnly=1 which causes the asm strings
in the pseudos to be ignored. I think this is why the aliases are
needed at all.

Reviewed By: frasercrmck

Differential Revision: https://reviews.llvm.org/D94024