ANDROID: net: rfkill: Introduce CONFIG_RFKILL_PM and use instead of CONFIG_PM to power down

Some platforms do not want to power down rfkill devices on suspend.

Change-Id: I62a11630521c636d54a4a02ab9037a43435925f5
Signed-off-by: Nick Pelly <npelly@google.com>

[AmitP: Folded following android-4.9 commit changes into this patch
        faad2b874fea ("rfkill: fix unused function warning")]
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>