Maxim has used the same clock IP on multiple PMICs like MAX77686,
MAX77802, MAX77620. Only differences are the number of clocks
from these PMICs like MAX77686 has 3 clocks output, MAX776802 have
two clock output and MAX77620 has one clock output.

Add clock binding details and DT example for the MAX77620.
Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
CC: Krzysztof Kozlowski <k.kozlowski@samsung.com>
CC: Javier Martinez Canillas <javier@dowhile0.org>
Reviewed-by: Javier Martinez Canillas <javier@osg.samsung.com>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>