rtc: generic: remove get_rtc_time/set_rtc_time wrappers

All architectures using this driver are now converted to
provide their own operations, so this one can be turned
into a trivial stub driver relying on its platform data.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>