rtc: fsl-ftm-alarm: remove select FSL_RCPM and default y from Kconfig

rtc: fsl-ftm-alarm: remove select FSL_RCPM and default y from Kconfig

The Flextimer alarm is primarily used as a wakeup source for system
power management.  But it shouldn't select the power management driver
as they don't really have dependency of each other.

Also remove the default y as it is not a critical feature for the
systems.

Signed-off-by: Li Yang <leoyang.li@nxp.com>
Link: https://lore.kernel.org/r/1573252856-11759-1-git-send-email-leoyang.li@nxp.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>