Introduce Rbit for instruction clarity

This commit introduces Rbit Enum. It improves accuracy within the APFv6
context. In APFv6, the Rbit doesn't always directly indicate register
usage.

Bug: 320199082
Test: TH
Change-Id: I1c26e364a99d83f3fa1edbadbd391ebdbfba2c3c
1 file changed