drm/i915/psr: Mask PSR irq bits when re-enabling interrupts.

gen8_de_irq_postinstall() wasn't masking the IRQ bit before passing the
debug flag to psr_irq_control(). This check was missed when new debug bits
were defined in  'commit c44301fc ("drm/i915: Allow control of PSR at
runtime through debugfs, v6")'. Instead of ANDing the irq bit in all the
callers, move it to the callee.

v2: Rebased.

Fixes: c44301fc ("drm/i915: Allow control of PSR at runtime through
debugfs, v6")
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180821221156.2442-3-dhinakaran.pandiyan@intel.com