[media] v4l: ti-vpe: Add helpers for creating VPDMA descriptors

Create functions which the VPE driver can use to create a VPDMA
descriptor and add it to a VPDMA descriptor list. These functions take a
pointer to an existing list, and append the configuration/data/control
descriptor header to the list.

In the case of configuration descriptors, the creation of a payload
block may be required(the payloads can hold VPE MMR values, or scaler
coefficients). The allocation of the payload buffer and it's content is
left to the VPE driver. However, the VPDMA library provides helper
macros to create payload in the correct format.

Add debug functions to dump the descriptors in a way such that it's easy
to see the values of different fields in the descriptors.

Signed-off-by: Archit Taneja <archit@ti.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Kamil Debski <k.debski@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>