clk: mmp2: Add the I2S clocks

A pair of fractional clock sources for PLLs and gates.

Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Link: https://lkml.kernel.org/r/20200519224151.2074597-8-lkundrak@v3.sk


Signed-off-by: Stephen Boyd <sboyd@kernel.org>