We want to wait dma fences in dirtyfb ioctl. As we don't want to make
dirtyfb ioctl as blocking call we need to use
dma_fence_add_callback. Callback used for dma_fence_add_callback is
called from atomic context. Due to this we need to add a new
frontbuffer tracking interface to queue flush.

v3:
 - Check schedule work success rather than work being pending
 - Init flush work when frontbuffer struct is initialized
v2: Check if flush work is already pending
Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230901093500.3463046-4-jouni.hogander@intel.com