setup_board: Add selinux POLICY_TYPES to make.conf

Container Linux only uses the mcs policy type, so add that to
portage/make.conf.

Signed-off-by: Geoff Levand <geoff@infradead.org>

Author: glevand

setup_board

@@ -265,6 +265,9 @@ PORTAGE_BINHOST="${BOARD_BINHOST}"
 # You can use --select to override this.
 EMERGE_DEFAULT_OPTS="--oneshot"
 
+# SELinux installed policies.
+POLICY_TYPES="mcs"
+
 # Allow the user to override or define additional settings.
 source "${BOARD_ETC}/portage/make.conf.user"
 EOF