rtc: fsl-ftm-alarm: add FTM alarm driver

For the platforms including LS1012A, LS1021A, LS1028A, LS1043A,
LS1046A, LS1088A, LS208xA that has the FlexTimer
module, implementing alarm functions within RTC subsystem
to wakeup the system when system going to sleep (work with RCPM driver).

Signed-off-by: Biwen Li <biwen.li@nxp.com>
Link: https://lore.kernel.org/r/20190813030157.48590-1-biwen.li@nxp.com


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>