clk: mediatek: Add MT2701 clock support

Add MT2701 clock support, include topckgen, apmixedsys,
infracfg, pericfg and subsystem clocks.

Signed-off-by: Shunli Wang <shunli.wang@mediatek.com>
Signed-off-by: James Liao <jamesjj.liao@mediatek.com>
Signed-off-by: Erin Lo <erin.lo@mediatek.com>
Tested-by: John Crispin <blogic@openwrt.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>