This patch cleans up and fixes issues in the M-Class system register handling:
1. It defines the system registers and the encoding (SYSm values) in one place:
a new ARMSystemRegister.td using SearchableTable, thereby removing the
hand-coded values which existed in multiple places.
2. Some system registers e.g. BASEPRI_MAX_NS which do not exist were being allowed!
Ref: ARMv6/7/8M architecture reference manual.
Reviewed by: @t.p.northover, @olist01, @john.brawn
Differential Revision: https://reviews.llvm.org/D35209
llvm-svn: 308456
Javed Absar