arm64: extend ESR/SPSR registers to 64b

For the Exception Syndrome Register, ESR_ELx, the upper 32b were
previously unused, but now may contain additional exception info as of
Armv8.7 (FEAT_LS64).

Extend ESR from u32->u64 in exception handling code to support this. In
addition, also extend Saved Program Status Register SPSR_ELx in the same
way to allow for future extensions.

Reviewed by: andrew
Sponsored by: Arm Ltd
Differential Revision: https://reviews.freebsd.org/D38983