mk: fix kernel modules build dependency

mk: fix kernel modules build dependency

Some kernel modules may need some header files to be "installed"
in the build directory.

When running multiple threads of make, kernel modules can try to
be compiled before the lib headers are ready:
	make -j3
	kernel/linux/kni/kni_misc.c:19:37: fatal error:
		exec-env/rte_kni_common.h: No such file or directory

This error appeared recently after moving kernel modules in their
own directory.

Fixes: acaa9ee991b5 ("move kernel modules directories")

Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Acked-by: Ferruh Yigit <ferruh.yigit@intel.com>