rtc: qpnp-rtc: Add support for thaw callback

Hibernation may fail after this driver's freeze
callback. Implement thaw callback to undo the
changes done in freeze callback.

Change-Id: I6ba6c2e51cdfc6e82fe0a6c1b1bab5e286a3716b
Signed-off-by: Atul Raut <araut@codeaurora.org>