gfx: fix local screen blank out with rapid hotplug/unplugs

gfx: fix local screen blank out with rapid hotplug/unplugs

Local display blanks out with too many rapid hot-plug/unplugs. This is
due to the call to drm_disable_unused_functions from the bottom-half irq
handler. This ends up as a race condition for this function which is called
once from drm and once from the bottom-half causing local display to get
into bad state.

Issue: HSD 207129
Signed-off-by: Amit Bhanagay <amit.bhanagay@intel.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>