drivers/rtc/rtc-pl031.c: add wakeup support

Mark the pl031 as wake-up capable so that rtcwake and suspend test can work.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Cc: Srinidhi Kasagar <srinidhi.kasagar@stericsson.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
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>