Setup the Amlogic FBC decoder for the VD1 video overlay plane.

The VD1 Amlogic FBC decoder is integrated in the pipeline like the
YUV pixel reading/formatter but used a direct memory address instead.

This adds support for the basic layout, and needs to calculate the content
body size since the header is allocated after.
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Tested-by: Kevin Hilman <khilman@baylibre.com>
Reviewed-by: Kevin Hilman <khilman@baylibre.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200703080728.25207-4-narmstrong@baylibre.com