arch: arm: soc: Cleanup Kconfig inclusion per SoC

When we included SoC specific Kconfig files we do something like:

gsource "arch/arm/soc/arm/*/Kconfig.soc"

However, we should do that inside an if block for that SoC family so as
to limit SoC family specific options to only being visible when that SoC
family is selected.  So we simply move the gsource and related items
inside the if SOC_FAMILY_<SOC> block.

Fixes: #7452

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>