[ARM] pxa: stop doing our own rtc management over suspend

Remove the RTC management over a suspend/resume cycle.  Firstly,
we may not be using the internal RTC for time keeping; some
platforms have an external RTC for this inspite of the PXA having
an internal RTC.  Secondly, the RTC library code handles updating
system time on resume.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>