omap4_panda: Disable ext2/3/4 support in SPL

Pandaboard is growing again, disable EXT2/3/4 support in SPL save more
space.

Signed-off-by: Tom Rini <trini@konsulko.com>

configs/omap4_panda_defconfig

 CONFIG_ARM=y
 CONFIG_OMAP44XX=y
+# CONFIG_SPL_EXT_SUPPORT is not set
 # CONFIG_SPL_I2C_SUPPORT is not set
 # CONFIG_SPL_NAND_SUPPORT is not set
 CONFIG_TARGET_OMAP4_PANDA=y