rtc: Remove Maxim 77802 driver

The max77686 RTC driver now supports the max77802 RTC as
well so there's no need to have a separate driver anymore.

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