drivers: modem: bg9x: Fix unused configs
drivers: modem: bg9x: Fix unused configs

Fix Kconfig so that unused configs won't be compiled.

Signed-off-by: Yong Cong Sin <d1951b00420cc51c2da597170bb83d89fa46ae3b@gmail.com>

zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,galak/zephyr,finikorg/zephyr,finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,galak/zephyr,finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr