ARM: omapl138_lcdk: Disable SPL_DM_USB

The USB was just recently enabled, so it is unlikely anyone is
using it in SPL, so this patch removes it from SPL to further
reduce the SPL code size.

Signed-off-by: Adam Ford <aford173@gmail.com>
diff --git a/configs/omapl138_lcdk_defconfig b/configs/omapl138_lcdk_defconfig
index d2342c3..63ed4e7 100644
--- a/configs/omapl138_lcdk_defconfig
+++ b/configs/omapl138_lcdk_defconfig
@@ -61,6 +61,7 @@
 CONFIG_SYS_NS16550=y
 CONFIG_USB=y
 CONFIG_DM_USB=y
+# CONFIG_SPL_DM_USB is not set
 CONFIG_USB_OHCI_HCD=y
 CONFIG_USB_OHCI_DA8XX=y
 CONFIG_USB_MUSB_HOST=y