Add MT7981 clock support, include topckgen, apmixedsys, infracfg and
ethernet subsystem clocks.
The drivers are based on clk-mt7981.c which can be found in MediaTek's
SDK sources. To be fit for upstream inclusion the driver has been split
into clock domains and the infracfg part has been significantly
de-bloated by removing all the 1:1 factors (aliases).
Signed-off-by: Jianhui Zhao <zhaojh329@xxxxxxxxx>
Signed-off-by: Daniel Golle <daniel@xxxxxxxxxxxxxx>