[media] media: ti-vpe: vpdma: allocate and maintain hwlist

VPDMA block used in ti-vip and ti-vpe modules have support for
up to 8 hardware descriptor lists. A descriptor list can be
submitted to any of the 8 lists (as long as it's not busy).

When multiple clients want to transfer data in parallel, its easier
to allocate one list per client and let it use it. This way, the
list numbers need not be hard-coded into the driver.

Add support for allocating hwlist and maintain them with a priv data.

Signed-off-by: Nikhil Devshatwar <nikhil.nd@ti.com>
Signed-off-by: Benoit Parrot <bparrot@ti.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>