thermal: hisi_termal: Switch from CONFIG_PM_SLEEP guards to pm_sleep_ptr()

Cleaning up the driver to use pm_sleep_ptr() macro instead of #ifdef
guards is simpler and allows the compiler to remove those functions
if built without CONFIG_PM_SLEEP support.

Signed-off-by: Hesham Almatary <hesham.almatary@huawei.com>
Reviewed-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>