Read fault address on arm64 using proposed kernel API.

On aarch64, the top 8 bits of the address (i.e. the tag bits) of
the fault address in si_addr are always clear. This isn't ideal for
MTE which will require these bits in order to correctly diagnose
tag mismatches.

A proposed kernel patch [1] exposes the full fault address including
the tag bits as part of the ucontext. Change debuggerd to read this
fault address if available.

[1] https://patchwork.kernel.org/patch/11435077/

Bug: 135772972
Change-Id: Ia05be574113860f4e9ecc36a310c4b740e0c4afb