The genrtc driver serves no purpose on mn10300 because it drives the
same hardware as the original rtc.c driver, and the newer rtc-generic.c
or rtc-cmos.c drivers on architectures that use the asm-generic/rtc.h
header.
I assume it was initially only added for completeness when the
mn10300 port was done, but the older rtc.c driver was always used
instead.
We can also stop include asm-generic/rtc.h now, because we
just call mc146818_set_time() directly.
It would be nice to change the architecture to use the rtc-cmos driver
next, and remove support for the old rtc driver as well.