drm/xe: Fix an invalid locking wait context bug

We cannot have spin locks around xe_irq_reset, since it will
call the intel_display_power_is_enabled() function, and
that needs a mutex lock. Hence causing the undesired
"[ BUG: Invalid wait context ]"

We cannot convert i915's power domain lock to spin lock
due to the nested dependency of non-atomic context waits.

So, let's move the xe_irq_reset functions from the
critical area, while still ensuring that we are protecting
the irq.enabled and ensuring the right serialization
in the irq handlers.

v2: On the first version, I had missed the fact that
irq.enabled is checked on the xe/display glue layer,
and that i915 display code is actually using the irq
spin lock properly. So, this got changed to a version
suggested by Matthew Auld.

v3: do not use lockdep_assert for display glue.
    do not save restore irq from inside IRQ or we can
    get bogus irq restore warnings

Closes: drm/xe/kernel#463


Suggested-by: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>