kbuild: deb-pkg: squash scripts/package/deb-build-option to debian/rules

The binary-arch target needs to use the same CROSS_COMPILE as used in
build-arch; otherwise, 'make run-command' may attempt to resync the
.config file.

Squash scripts/package/deb-build-option into debian/rules, as it is a
small amount of code.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <n.schier@avm.de>