makefile: hook up dpdkstrip preprocessor

makefile: hook up dpdkstrip preprocessor

When building the openvswitch-custom.te file, it is important to have the
ability to filter out dpdk blocks depending on whether the system has been
configured with dpdk or not.  This allows using all the standard .in file
blocks, as well as the dpdkstrip blocks, when constructing the selinux
policy file.

Additionally, this means any .in files which might want to change based on
configuration to exclude blocks based on dpdk can do so.

Acked-by: Flavio Leitner <fbl@sysclose.org>
Acked-by: Ansis Atteka <aatteka@ovn.org>
Signed-off-by: Aaron Conole <aconole@redhat.com>
Tested-by: Jean Hsiao <jhsiao@redhat.com>