kconfig: libmetal: Have LIBMETAL_SRC_PATH depend on LIBMETAL
kconfig: libmetal: Have LIBMETAL_SRC_PATH depend on LIBMETAL

Kconfig options are often either of the type 'feature' or
'configuration'. Meaning, either an option controls whether a feature
is enabled, or it adjusts/configures an already enabled feature.

Configuration of features should depend on the feature they are
configuring or else noise is created both in the Kconfig output and in
the Kconfig menu.

In this commit we add a dependency from a configuration option to it's
feature option.

Signed-off-by: Sebastian Bøe <edee888afd63e94916688495334700803eba20a0@nordicsemi.no>

punitvara/zephyr,GiulianoFranchetto/zephyr,zephyrproject-rtos/zephyr,ldts/zephyr,finikorg/zephyr,galak/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,galak/zephyr,ldts/zephyr,punitvara/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,finikorg/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,explora26/zephyr,explora26/zephyr,explora26/zephyr,Vudentz/zephyr,explora26/zephyr,galak/zephyr,nashif/zephyr,nashif/zephyr,finikorg/zephyr,ldts/zephyr,nashif/zephyr,GiulianoFranchetto/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,Vudentz/zephyr,nashif/zephyr,nashif/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,punitvara/zephyr,ldts/zephyr,zephyrproject-rtos/zephyr,punitvara/zephyr,explora26/zephyr,punitvara/zephyr,GiulianoFranchetto/zephyr,ldts/zephyr