This is part 3 of 3 of the genrtc patches.  This is my own slight bit
of work, as well as some work by Randolph Chung. This changes
set_rtc_time(struct *rtc_time) to return an int instead of void.
This was done so that the arch-specific code here could do additional
checks on the time and return an error if needed. This then introduces
include/asm-generic/rtc.h, include/asm-i386/rtc.h and
include/asm-alpha/rtc.h.  include/asm-generic/rtc.h contains the
get_rtc_time and set_rtc_time logic that is in drivers/char/rtc.c and
has been tested on SMP i386.  This also modifies include/asm-ppc/rtc.h
to return -ENODEV if no rtc hardware is present.

Additionally, Dave Jones pointed out to me a place where we might not be
safe when jiffies wraps, so this switches that to time_after().

From Randolph Chung, support for a 64bit kernel and a 32bit userland.