dra7xx_evm: Enabled UART-boot mode and add dra7xx_evm_uart3 build

UART booting is supported on this SoC, but via UART3 rather than UART1.
Because of this we must change the board to use UART3 for all console
access (only one UART is exposed on this board and a slight HW mod is
required to switch UARTs).

Signed-off-by: Minal Shah <minal.shah@ti.com>
[trini: Make apply to mainline, reword commit]
Signed-off-by: Tom Rini <trini@ti.com>
diff --git a/arch/arm/include/asm/arch-omap5/spl.h b/arch/arm/include/asm/arch-omap5/spl.h
index 57f0de5..2d5a62e 100644
--- a/arch/arm/include/asm/arch-omap5/spl.h
+++ b/arch/arm/include/asm/arch-omap5/spl.h
@@ -16,6 +16,7 @@
 #define BOOT_DEVICE_MMC2        6
 #define BOOT_DEVICE_MMC2_2	7
 #define BOOT_DEVICE_SPI		10
+#define BOOT_DEVICE_UART	0x43
 
 #define MMC_BOOT_DEVICES_START	BOOT_DEVICE_MMC1
 #define MMC_BOOT_DEVICES_END	BOOT_DEVICE_MMC2_2