arm64: sysreg: Add some field definitions for PAR_EL1

PAR_EL1 is a mysterious creature, but sometimes it's necessary to read
it when translating addresses in situations where we cannot walk the
page table directly.

Add a couple of system register definitions for the fault indication
field ('F') and the fault status code ('FST').

Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>