clk: max77686: Add DT binding details for PMIC MAX77620

clk: max77686: Add DT binding details for PMIC MAX77620

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>
(cherry picked from commit e581245d8aaf897870afacd4aaf2bbce77cf1f1e)
Signed-off-by: Venkat Reddy Talla <vreddytalla@nvidia.com>
Change-Id: I75845e515c1b1999650ea33f5d7a505efbad010d
Reviewed-on: http://git-master/r/1310953
GVS: Gerrit_Virtual_Submit
Reviewed-by: Venkat Reddy Talla <vreddytalla@nvidia.com>
Tested-by: Venkat Reddy Talla <vreddytalla@nvidia.com>
Reviewed-by: Laxman Dewangan <ldewangan@nvidia.com>