TI:OMAP4: enable EXT support in SPL for OMAP4 boards

Enable EXT support in SPL for OMAP4 boards.
Build tested for duovero, omap4_sdp4430 and omap4_panda.
Run time tested on omap4_panda.

Signed-off-by: Guillaume GARDET <guillaume.gardet@free.fr>
Cc: Tom Rini <trini@ti.com>

include/configs/ti_omap4_common.h

@@ -167,6 +167,9 @@
 #define CONFIG_SYS_SPL_ARGS_ADDR	(CONFIG_SYS_SDRAM_BASE + \
 					 (128 << 20))
 
+/* SPL: Allow to use an EXT partition */
+#define CONFIG_SPL_EXT_SUPPORT
+
 #ifdef CONFIG_NAND
 #define CONFIG_SPL_NAND_AM33XX_BCH	/* ELM support */
 #endif