selftests: arm64: add test for unaligned/inexact watchpoint handling

ARM64 hardware expects 64bit aligned address for watchpoint invocation.
However, it provides byte selection method to select any number of
consecutive byte set within the range of 1-8.

This patch adds support to test all such byte selection option for
different memory write sizes.

Patch also adds a test for handling the case when the cpu does not
report an address which exactly matches one of the regions we have
been watching (which is a situation permitted by the spec if an
instruction accesses both watched and unwatched regions). The test
was failing on a MSM8996pro before this patch series and is
passing now.

Signed-off-by: Pavel Labath <labath@google.com>
Signed-off-by: Pratyush Anand <panand@redhat.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>