Staging: rtl8192e: Use the standard config option for PM functions

Use the standard config option CONFIG_PM to enable rtl8192e PM
functions. Tested on Samsung N140 and it works fine. Without enabling
the PM functions, the box always fails to resume.

Signed-off-by: Yong Wang <yong.y.wang@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>