mipi_dbi_enable_flush() wants to call the fb->dirty() hook from the
bowels of the .atomic_enable() hook. That prevents us from taking the
plane mutex in fb->dirty() unless we also plumb down the acquire
context.

Instead it seems simpler to split the fb->dirty() into a tinydrm
specific lower level hook that can be called from
mipi_dbi_enable_flush() and from a generic higher level
tinydrm_fb_dirty() helper. As we don't have a tinydrm specific
vfuncs table we'll just stick it into tinydrm_device directly
for now.

v2: Deal with the fb->dirty() in tinydrm_display_pipe_update() as well (Noralf)

Cc: "Noralf Trønnes" <noralf@tronnes.org>
Cc: David Lechner <david@lechnology.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Noralf Trønnes <noralf@tronnes.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20180323153509.15287-1-ville.syrjala@linux.intel.comReviewed-by: Noralf Trønnes <noralf@tronnes.org>
Tested-by: Noralf Trønnes <noralf@tronnes.org>