[llvm][readobj] Add AArch64 SME and SME2 note types
These are used to store new state added by the Scalable Matrix
Extension which is documented in
https://developer.arm.com/documentation/ddi0616/aa/.
The values match those defined by Linux, see:
https://github.com/torvalds/linux/blob/
e62252bc55b6d4eddc6c2bdbf95a448180d6a08d/include/uapi/linux/elf.h#L435
The ZT register(s) are added by SME2 which is not yet publicly
documented but has support in LLVM and Linux already.
Also added descriptions for SVE and PAC_MASK notes since those
were missing.
Reviewed By: jhenderson
Differential Revision: https://reviews.llvm.org/D148126