linux-phytec-ti

drm/omap: add WB support

The OMAP DSS supports writing back the display unit output to memory.
Although it support several modes, this driver introduces the use
of the write-back (WB) feature as a method to perform memory 2 memory
frame conversion (M2M) and as a method to capture frame from a
specific active overlay manager (CAP).

Since the M2M and CAP method both make use of a single H/W IP
resource a single thin layer is also added to ease the
integration into the drm framework and provide common helpers.

Only one of the currently supported methods can be active at a time.
Access to the WB resource is mitigated at the video node level
where each access method will provide its own video device node
but only one will be able to be opened at a time.

If WB is currently assigned to one device node then attempts to open
the other device node will return EBUSY.

Signed-off-by: Benoit Parrot <bparrot@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>