drivers/rtc/rtc-tegra.c: protect suspend/resume callbacks with CONFIG_PM_SLEEP

CONFIG_PM doesn't actually enable any of the PM callbacks, it only allows
to enable CONFIG_PM_SLEEP and CONFIG_PM_RUNTIME.  This means if CONFIG_PM
is used to protect system sleep callbacks then it may end up unreferenced
if only runtime PM is enabled.  Hence protecting sleep callbacks with
CONFIG_PM_SLEEP.

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Reviewed-by: Thierry Reding <thierry.reding@avionic-design.de>
Reviewed-by: Stephen Warren <swarren@nvidia.com>
Cc: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>