arm64: Add MOPS implementations of memset(), memcpy() and memmove()

[sarah.walker2_arm.com]

Summary

Enable the use of MOPS implementations of memset, memcpy and memmove within
the kernel. Fix pre-ifunc resolution uses of these functions.

Sponsored by: Arm Ltd

[andrew]

I think we will need to also update the calls to memset/bzero in pmap_bootstrap_*. These functions are used by the kernel sanitizers to build the early shadow region.