In current kernel if we want to set the alarm time, the absolute time the
seconds relative to 1970-01-01 00:00:00) should be written into
/sys/class/rtc/rtc0/wakealarm.  It is not convenient.

It is more reasonable to add the support for the alarm time relative to
current RTC time.(the unit is second)

For example:
If the RTC is required to generate alarm after 2 minutes, the following
will be OK.
	echo +120 > /sys/class/rtc/rtc0/wakealarm
or      echo +0x78 > /sys/class/rtc/rtc0/wakealarm
Signed-off-by: Zhao Yakui <yakui.zhao@intel.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>