drm/ingenic: Simplify code by using hwdescs array

Instead of having one 'hwdesc' variable for the plane #0, one for the
plane #1 and one for the palette, use a 'hwdesc[3]' array, where the
DMA hardware descriptors are indexed by the plane's number.

v2: dma_hwdesc_addr() extended to support palette hwdesc. The palette
    hwdesc is now hwdesc[3] to simplify things. Add
    ingenic_drm_configure_hwdesc*() functions to factorize code.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20211026181240.213806-2-paul@crapouillou.net


Tested-by: Nikolaus Schaller <hns@goldelico.com>
Reviewed-by: Christophe Branchereau <cbranchereau@gmail.com>