Add AARCH64 syntax support (part 1)

- Registers:

 - general purpose: x0-x30, sp, pc
 - general purpose 32 bit: w0-w30, wsp
 - "zero registers": wzr, xzr
 - floating point q15-q31

Instructions:

System:
 - ret,iret,eret
 - wfi

Branches:

 - conditional: B.cond where cond is one of standard condition suffixes
 - compare and branch: CBNZ, CBZ, TBNZ, TBZ,

Load/Store:
 - pairs: stp/ldp