clk: sunxi: Add display and TCON0 clocks driver

The A10 SoCs and its relatives has a special clock controller to drive the
display engines (both frontend and backend), that have a lot in common with
the clock to drive the first TCON channel.

Add a driver to support both.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Rob Herring <robh@kernel.org>
[sboyd@codeaurora.org: Silence variable sized array warning]
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>