[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