drm/imagination: avoid deadlock on fence release

In the Linux kernel, the following vulnerability has been resolved:

drm/imagination: avoid deadlock on fence release

Do scheduler queue fence release processing on a workqueue, rather

than in the release function itself.

Fixes deadlock issues such as the following:

[ 607.400437] ============================================

[ 607.405755] WARNING: possible recursive locking detected

[ 607.415500] --------------------------------------------

[ 607.420817] weston:zfq0/24149 is trying to acquire lock:

[ 607.426131] ffff000017d041a0 (reservation_ww_class_mutex){+.+.}-{3:3}, at: pvr_gem_object_vunmap+0x40/0xc0 [powervr]

[ 607.436728]

but task is already holding lock:

[ 607.442554] ffff000017d105a0 (reservation_ww_class_mutex){+.+.}-{3:3}, at: dma_buf_ioctl+0x250/0x554

[ 607.451727]

other info that might help us debug this:

[ 607.458245] Possible unsafe locking scenario:

[ 607.464155] CPU0

[ 607.466601] ----

[ 607.469044] lock(reservation_ww_class_mutex);

[ 607.473584] lock(reservation_ww_class_mutex);

[ 607.478114]

*** DEADLOCK ***