OMAP3EVM: Set default bootfile

The current configuration doesn't define default
bootfile; leading to this warning at execution:

OMAP3_EVM # dhcp
...
...
DHCP client bound to address 192.168.1.11
*** Warning: no boot file name; using 'AC18BE16.img'
TFTP from server 0.0.0.0; our IP address is 192.168.1.11;
sending through gateway 192.168.1.1
Filename 'AC18BE16.img'.
Load address: 0x82000000
Loading: *
TFTP error: 'File not found' (1)
Signed-off-by: NSanjeev Premi <premi@ti.com>

include/configs/omap3_evm.h

@@ -149,6 +149,8 @@
 /* Environment information */
 #define CONFIG_BOOTDELAY	10
 
+#define CONFIG_BOOTFILE		uImage
+
 #define CONFIG_EXTRA_ENV_SETTINGS \
 	"loadaddr=0x82000000\0" \
 	"console=ttyS2,115200n8\0" \