clk: mediatek: Add dt-bindings for MT2712 clocks

Add MT2712 clock dt-bindings, include topckgen, apmixedsys,
infracfg, pericfg, mcucfg and subsystem clocks.

Signed-off-by: Weiyi Lu <weiyi.lu@mediatek.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>