The 'ELPM' instruction has three forms:
--------------------------
| form | feature |
| ----------- | -------- |
| ELPM | hasELPM |
| ELPM Rd, Z | hasELPMX |
| ELPM Rd, Z+ | hasELPMX |
--------------------------
The second form is always used in the expansion of pseudo instructions
LPMWRdZ/ELPMWRdZ. But for devices without ELPMX and with only ELPM,
only the first form can be used.
Reviewed By: aykevl, Miss_Grape
Differential Revision: https://reviews.llvm.org/D141264
acb4d143bd