rtc: max77686: Add max77802 support

The MAX77686 and MAX77802 RTC IP blocks are very similar with only
these differences:

0) The RTC registers layout and addresses are different.

1) The MAX77686 use 1 bit of the sec/min/hour/etc registers as the
   alarm enable while MAX77802 has a separate register for that.

2) The MAX77686 RTCYEAR register valid values range is 0..99 while
   for MAX77802 is 0..199.

3) The MAX77686 has a separate I2C address for the RTC registers
   while the MAX77802 uses the same I2C address as the PMIC regs.

5) The minimum delay before a RTC update (16 msecs vs 200 usecs).

There are separate drivers for MAX77686 and MAX77802 RTC IP blocks
but the differences are not that big so the driver can be extended
to support both instead of duplicating a lot of code in 2 drivers.

Suggested-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Acked-by: Laxman Dewangan <ldewangan@nvidia.com>
Tested-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Reviewed-by: Andi Shyti <andi.shyti@samsung.com>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>