x86, hibernate: Rename temp_level4_pgt to temp_pgt

As 32bit system is not using 4-level page, rename it
to temp_pgt so that it can be reused for both 32bit
and 64bit hibernation.

No functional change.

Signed-off-by: Zhimin Gu <kookoo.gu@intel.com>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>