Remove /boot/efi from mtree, missed in 0b7472b3d8.

This had prevented the bootconfig step from determining if an ESP exists,
resulting in its unconditional setup. On BIOS-booted amd64, this wasn't
harmful, just unnecessary, but it resulted in failed installations on
non-EFI-supporting platforms like powerpc64.

MFC after:	3 days

etc/mtree/BSD.root.dist

@@ -18,8 +18,6 @@
             rockchip              tags=package=runtime
             ..
         ..
-        efi
-        ..
         firmware
         ..
         loader.conf.d             tags=package=bootloader

release/tools/arm.subr

@@ -184,6 +184,7 @@ arm_install_base() {
 		TARGET_ARCH=${EMBEDDED_TARGET_ARCH} \
 		DESTDIR=${DESTDIR} KERNCONF=${KERNEL} \
 		${CONF_FILES} installworld installkernel distribution
+	chroot ${CHROOTDIR} mkdir -p ${DESTDIR}/boot/efi
 	chroot ${CHROOTDIR} mkdir -p ${DESTDIR}/boot/msdos
 
 	arm_create_user