clk: max77686: Add support for MAX77620 clocks

Maxim Max77620 has one 32KHz clock output and the clock HW
IP used on this PMIC is same as what it is there in the MAX77686.

Add clock driver support for MAX77620 on the MAX77686 driver.

CC: Krzysztof Kozlowski <k.kozlowski@samsung.com>
CC: Javier Martinez Canillas <javier@dowhile0.org>
Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Tested-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Reviewed-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>