arm64: suspend: Initialize PMR on resume

When we resume from cpu_suspend() context tracking, specially,
ct_idle_exit() performs IRQ save/restore sequence. It doesn't cause
any functional issues since we have masked all exceptions prior
suspend and have not restored them. However, in case of pseudo-NMI PMR
can be set by firmware to arbitrary value, thus IRQ save/restore
routines manipulates this arbitrary value. Again, it doesn't cause any
issues since PMR variant of IRQ save helper carries a
__pmr_irqs_disabled_flags() guard.

Going forward __pmr_irqs_disabled_flags() guard will be gone and we
will call __pmr_local_irq_disable() unconditionally - that would cause
warning in case CONFIG_ARM64_DEBUG_PRIORITY_MASKING is set.

Initialize PMR to a value known to Linux on resume until the normal
exception restore path restores the saved DAIF and PMR state.

Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>

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