Fix Kbuild to enable WLAN debugfs support

Currently, the CONFIG_WLAN_POWER_DEBUGFS and CONFIG_WLAN_DEBUGFS
are not enabled for statically loaded driver.
This results in missing subsystem power stats.
The reason for that is the enabling of this macro is conditionally
done under KERNEL_BUILD=0.
This commit enables the macro to be also
conditionally done under all values of KERNEL_BUILD

Bug: 29339696
Test: manual
Change-Id: I9b0ade71923d97cbb899efb2c4697bc912cf5a8b
Signed-off-by: Ahmed ElArabawy <arabawy@google.com>