The SpecialValue field used in the disassembler covers too wide a range,
this causes some duplication in the disassembler of instructions like
mov, since the SpecialValue includes a bit used for the immediate.

Attempt to refactor and follow the decoding guide given in the
architecture manual [0], F4.1 A32 instruction set encoding, with the
eventual goal for removing the duplicated instruction disassembly.

[0] ARM DDI 0487F.b ARMv8 A32 instruction set

Bug: v8:10933
Change-Id: Iddf4df317f9a5b29be2544ad2f9f93180e9bcdfc
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2497395
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70775}