rtc: cmos: remove empty asm/mc146818rtc.h files

Nothing on these architectures ever includes the asm/mc146818rtc.h
file, the drivers that used to do this have been fixed long ago,
and the remaining users are all PC-specific.

This removes the files for good.

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>