arm64: mte: configure initial state for system registers

The fields in SCTLR_EL1 and HCR_EL2 for enabling MTE are set, and if the
ID_AA64PFR1_EL1 register shows MTE is present, the GCR_EL1 register is
also configured, and the two TFSR registers which hold pending tag check
faults are cleared.

Reviewed by: andrew
Sponsored by: Arm Ltd
Signed-off-by: Harry Moulton <harry.moulton@arm.com>
Differential Revision: https://reviews.freebsd.org/D55946