ARM: Support PUSH and POP mnemonics

[Prcuvu]

In ARM mode, PUSH reglist is a synonym for STMDB sp!, reglist and POP reglist is a synonym for LDMIA sp!, reglist. When reading disassembly, PUSH and POP are important markers for subroutine entry and return.

This commit adds support to these mnemonics.

References

• ARM Compiler armasm User Guide Version 5.06 - PUSH
• ARM Compiler armasm User Guide Version 5.06 - POP

[MAP233224]

I didn't know they were the preferred mnemonics at the time, apparently they changed their mind because in the original PDF they didn't use PUSH nor POP in the ARM version of the instructions. I'll review the code later and this will probably get merged soon after :)

[Prcuvu]

Hello, it has been half a year. Is there anything blocking the review?