clk: mmp2: Add audio clock controller driver

This is a driver for a block that generates master and bit clocks for
the I2S interface. It's separate from the PMUs that generate clocks for
the peripherals.

Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Link: https://lkml.kernel.org/r/20200519224151.2074597-14-lkundrak@v3.sk
Signed-off-by: Stephen Boyd <sboyd@kernel.org>