[SystemZ] Allow specifying integer registers as part of the address calculation

[SystemZ] Allow specifying integer registers as part of the address calculation

Revision e1de2773a534957305d7a559c6d88c4b5ac354e2 provided support for
accepting integer registers in inline asm i.e.

__asm("lhi %r0, 5") -> lhi %r0, 5
__asm("lhi 0, 5") -> lhi 0,5

This patch aims to extend this support to instructions which compute
addresses as well. (i.e instructions of type BDMem and BD[X|R|V|L]Mem)

Author: anirudhp

Differential Revision: https://reviews.llvm.org/D83251