configs: am335x: usb: do not define CONFIG_DM_USB for spl

Since OMAP's spl doesn't support DM currently, do not define
CONFIG_DM_USB for spl build.

Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>

include/configs/am335x_evm.h

@@ -316,6 +316,7 @@
 #ifdef CONFIG_SPL_BUILD
 #undef CONFIG_DM_MMC
 #undef CONFIG_TIMER
+#undef CONFIG_DM_USB
 #endif
 
 #if defined(CONFIG_SPL_BUILD) && defined(CONFIG_SPL_USBETH_SUPPORT)