drm/gma500: Move asle interrupt work into a work task

Previously the backlight code was called from IRQ context which isn't
allowed. This patch moves all the asle work into a work task which takes
care of the locking bug reported by users.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=64221
Signed-off-by: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>

diff --cc drivers/gpu/drm/gma500/opregion.c
Simple merge

diff --cc drivers/gpu/drm/gma500/psb_drv.h
Simple merge