char/genrtc: remove mn10300 support

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.

[linux@roeck-us.net: Add missing include file to proc-init.c]
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>