imx: mx6sabresd discard PHYS_SDRAM_SIZE

This macro is not needed, since gd->ram_size is assigned value using
function imx_ddr_size().

Signed-off-by: Peng Fan <Peng.Fan@freescale.com>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Fabio Estevam <fabio.estevam@freescale.com>
Reviewed-by: Fabio Estevam <fabio.estevam@freescale.com>

include/configs/mx6sabresd.h

@@ -19,7 +19,6 @@
 #define CONFIG_MXC_UART_BASE	UART1_BASE
 #define CONFIG_CONSOLE_DEV		"ttymxc0"
 #define CONFIG_MMCROOT			"/dev/mmcblk1p2"
-#define PHYS_SDRAM_SIZE		(1u * 1024 * 1024 * 1024)
 
 #define CONFIG_SUPPORT_EMMC_BOOT /* eMMC specific */