ARM: AM43x: Fix MAX_RAM_BANK_SIZE

On AM437x-GP Evm there is 2GB of DDR3 memory available as stated in
AM437x GP EVM HardwareUser's guide http://www.ti.com/lit/ug/spruhw7/spruhw7.pdf

.
But MAX_RAM_BANK_SIZE is defined as 1GB.
Fixing MAX_RAM_BANK_SIZE to 2GB on AM43xx.

Reported-by: Shivasharan Nagalikar <shivasharan.nagalikar@ti.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>

include/configs/am43xx_evm.h

@@ -17,7 +17,7 @@
 #define CONFIG_BOARD_LATE_INIT
 #define CONFIG_ARCH_CPU_INIT
 #define CONFIG_SYS_CACHELINE_SIZE       32
-#define CONFIG_MAX_RAM_BANK_SIZE	(1024 << 20)	/* 1GB */
+#define CONFIG_MAX_RAM_BANK_SIZE	(1024 << 21)	/* 2GB */
 #define CONFIG_SYS_TIMERBASE		0x48040000	/* Use Timer2 */
 
 #include <asm/arch/omap.h>