dt-bindings: clk: sun5i: add DRAM gates compatible

The Allwinner SoCs have a gate controller to gate the access to the DRAM
clock to the some devices that need to access the DRAM directly (mostly
display / image related IPs).

Use a simple gates driver to support the one found in the A13 / R8 SoCs.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>