ACPI / PM: Remove unneeded nested #ifdef

In commit 5de21bb9 ("ACPI / PM: Drop CONFIG_PM_RUNTIME from the
ACPI core"), all occurrences of CONFIG_PM_RUNTIME were replaced with
CONFIG_PM. This created the following structure of #ifdef blocks in
the code:

 [...]
 #ifdef CONFIG_PM
 #ifdef CONFIG_PM
 /* always on / undead */
 #ifdef CONFIG_PM_SLEEP
 [...]
 #endif
 #endif
 [...]
 #endif

This patch removes the inner "#ifdef CONFIG_PM" block as it will
always be enabled when the outer block is enabled. This inconsistency
was found using the undertaker-checkpatch tool.

Signed-off-by: Andreas Ruprecht <rupran@einserver.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>