target.mk: improve handling of default enabled SECCOMP

target.mk: improve handling of default enabled SECCOMP

Handling default packages selection is really problematic and error
prone. In all the changes, the SECCOMP config is enabled by default if
supported by the target.

This is problematic for the scenario of the first .config creation where
this option will be enabled by default but the package default are
already being parsed.

This cause the reparsing of the default package on the next command and
the "outdated config" error. To better handle this special case, add
additiona logic to match the dependency in the config and check if
CONFIG_SECCOMP should be enabled by default in the scenario where a
.config needs to be init and doesn't exist.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>