aarch64: MTE compatible strcmp

aarch64: MTE compatible strcmp

Add support for MTE to strcmp. Regression tested with xcheck and benchmarked
with glibc's benchtests on the Cortex-A53, Cortex-A72, and Neoverse N1.

The existing implementation assumes that any access to the pages in which the
string resides is safe. This assumption is not true when MTE is enabled. This
patch updates the algorithm to ensure that accesses remain within the bounds
of an MTE tag (16-byte chunks) and improves overall performance.

Co-authored-by: Branislav Rankov <branislav.rankov@arm.com>
Co-authored-by: Wilco Dijkstra <wilco.dijkstra@arm.com>