dt-bindings: clock: Add support for the MSM8226 mmcc

Document the multimedia clock controller found on MSM8226.

Signed-off-by: Bartosz Dudziak <bartosz.dudziak@snejp.pl>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20220207185411.19118-2-bartosz.dudziak@snejp.pl