Documentation/process: maintainer-soc: Be more explicit about defconfig

Documentation/process: maintainer-soc: Be more explicit about defconfig

It is already documented but people still send noticeable amount of
patches ignoring the rule - get_maintainers.pl does not work on
arm64/configs/defconfig or any other shared ARM defconfig.

Be more explicit, that one must not rely on typical/simple approach
here for getting To/Cc list.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>
Reviewed-by: Linus Walleij <linusw@kernel.org>
Link: https://lore.kernel.org/r/20251223142726.73417-3-krzysztof.kozlowski@oss.qualcomm.com
Signed-off-by: Arnd Bergmann <arnd@arndb.de>