With the A80 SoC, Allwinner grouped and moved some subsystem specific
clock controls to a separate address space, and possibly separate
hardware block.

One such subsystem is the display engine. The main clock control unit
now only has 1 set of bus gate, dram gate, module clock, and reset
control for the entire display subsystem. These feed into a secondary
clock control unit, which has controls for each individual module
of the display pipeline. This block is not documented in the user
manual. Allwinner's kernel was used as the reference.

Add support for the display engine clock controls found on the A80.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>