rtc: Kconfig: select REGMAP_I2C when necessary

[ Upstream commit 578c2b661e2b1b474ea3571a3c3c6d57bae89e8d ]

Some i2c RTC drivers are using regmap but are not selecting REGMAP_I2C
which may lead to build failures.

Link: https://lore.kernel.org/r/20200127221724.10160-2-alexandre.belloni@bootlin.com


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>