Turn on some MIDI kernel modules.

Issue: ev3dev/ev3dev#726

arch/arm/configs/ev3dev_defconfig

@@ -171,7 +171,11 @@ CONFIG_LOGO=y
 # CONFIG_LOGO_LINUX_CLUT224 is not set
 CONFIG_SOUND=m
 CONFIG_SND=m
+CONFIG_SND_SEQUENCER=m
+CONFIG_SND_SEQ_DUMMY=m
+CONFIG_SND_HRTIMER=m
 # CONFIG_SND_VERBOSE_PROCFS is not set
+CONFIG_SND_VIRMIDI=m
 CONFIG_SND_USB_AUDIO=m
 CONFIG_HID_BATTERY_STRENGTH=y
 CONFIG_HIDRAW=y
@@ -202,6 +206,7 @@ CONFIG_USB_ETH=m
 CONFIG_USB_ETH_EEM=y
 CONFIG_USB_MASS_STORAGE=m
 CONFIG_USB_G_SERIAL=m
+CONFIG_USB_MIDI_GADGET=m
 CONFIG_USB_CDC_COMPOSITE=m
 CONFIG_MMC=y
 CONFIG_MMC_DAVINCI=y