hw: make all of hw/usb/ configurable via default-configs/

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/default-configs/arm-softmmu.mak b/default-configs/arm-softmmu.mak
index 2d53895..4b72019 100644
--- a/default-configs/arm-softmmu.mak
+++ b/default-configs/arm-softmmu.mak
@@ -30,6 +30,7 @@
 CONFIG_PFLASH_CFI01=y
 CONFIG_PFLASH_CFI02=y
 CONFIG_MICRODRIVE=y
+CONFIG_USB_MUSB=y
 
 CONFIG_ARM_TIMER=y
 CONFIG_PL011=y