build:always build and install the usb mass storage driver.

Change-Id: Ib54902a21443bd110bfc7498c00776831cbdefaf

http://gerrit.minix3.org/#/c/2693/

distrib/sets/lists/minix/mi

@@ -112,6 +112,7 @@
 ./etc/system.conf			minix-sys
 ./etc/system.conf.d			minix-sys
 ./etc/system.conf.d/ipc			minix-sys
+./etc/system.conf.d/usb_storage		minix-sys
 ./etc/termcap				minix-sys
 ./etc/ttys				minix-sys
 ./etc/utmp				minix-sys
@@ -4935,6 +4936,7 @@
 ./usr/sbin/tty				minix-sys
 ./usr/sbin/uds				minix-sys
 ./usr/sbin/unlink			minix-sys
+./usr/sbin/usb_storage			minix-sys
 ./usr/sbin/user				minix-sys
 ./usr/sbin/useradd			minix-sys
 ./usr/sbin/userdel			minix-sys

drivers/Makefile

@@ -13,6 +13,7 @@ SUBDIR= hello \
 	random \
 	tty \
 	uds \
+	usb_storage \
 	vnd \
 	readclock