arm64: make is_permission_fault() name clearer

The naming of is_permission_fault() makes it sound like it should return
true for permission faults from EL0, but by design, it only does so for
faults from EL1.

Let's make this clear by dropping el1 in the name, as we do for
is_el1_instruction_abort().

Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>