staging: wilc1000: move 'wilc_enable_ps' global variable into 'wilc' struct

Instead of having 'wilc_enable_ps' as global variable moved it to 'wilc'
structure. Rename 'wilc_enable_ps' to 'enable_ps' as its already part of
'wilc' structure

Signed-off-by: Ajay Singh <ajay.kathat@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>