mfd: sec: Add support for the RTC on S2MPA01

The RTC portion of the S2MPA01 appears to have the same
register layout as the S2MPS14.

Signed-off-by: Stuart Menefy <stuart.menefy@mathembedded.com>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>