MIPS: ralink: add RT5350 sdram register defines

Add a few missing defines that are needed to make memory detection work on the
RT5350.

Signed-off-by: John Crispin <[e-mail]>
Acked-by: Gabor Juhos <[e-mail]>
Patchwork: http://patchwork.linux-mips.org/patch/5169/

arch/mips/include/asm/mach-ralink/rt305x.h

···
 #define RT5350_SYSCFG0_CPUCLK_320	0x2
 #define RT5350_SYSCFG0_CPUCLK_300	0x3
 
+#define RT5350_SYSCFG0_DRAM_SIZE_SHIFT  12
+#define RT5350_SYSCFG0_DRAM_SIZE_MASK   7
+#define RT5350_SYSCFG0_DRAM_SIZE_2M     0
+#define RT5350_SYSCFG0_DRAM_SIZE_8M     1
+#define RT5350_SYSCFG0_DRAM_SIZE_16M    2
+#define RT5350_SYSCFG0_DRAM_SIZE_32M    3
+#define RT5350_SYSCFG0_DRAM_SIZE_64M    4
+
 /* multi function gpio pins */
 #define RT305X_GPIO_I2C_SD		1
 #define RT305X_GPIO_I2C_SCLK		2