dt-bindings: clock: Add MMP3 compatible string

This binding describes the PMUs that are found on MMP3 as well. Add the
compatible strings and adjust the description.

Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lkml.kernel.org/r/20200309194254.29009-7-lkundrak@v3.sk


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