[dbus] Add config for button backlight methods. JB#39838
[dbus] Add config for button backlight methods. JB#39838

The button backlight related dbus method are supposed to be available for
all process, but due to missing config only root processes are allowed to
make these method calls.

Add necessary dbus configuration to make the methods callable by everybody.

Signed-off-by: Simo Piiroinen <6d5e5360bed3d486f7d9fb26b0f737f7d4fd45ee@jollamobile.com>

spiiroin/mce,spiiroin/mce,spiiroin/mce,spiiroin/mce