ti_omap5_common: eth: do not define DM_ETH for spl

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

Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>

include/configs/ti_omap5_common.h

@@ -153,6 +153,7 @@
 #ifdef CONFIG_SPL_BUILD
 #undef CONFIG_DM_MMC
 #undef CONFIG_TIMER
+#undef CONFIG_DM_ETH
 #endif
 
 #endif /* __CONFIG_TI_OMAP5_COMMON_H */