mx23: Document the tRAS lockout setting in memory initialization

Add a comment about the tRAS lockout setting of HW_DRAM_CTL08 to
enable the 'Fast Auto Pre-Charge' found in the memory chip. The
setting is applied after memory initialization and it is worth
document it.
Signed-off-by: NOtavio Salvador <otavio@ossystems.com.br>

arch/arm/cpu/arm926ejs/mxs/spl_mem_init.c

@@ -120,6 +120,10 @@ static void initialize_dram_values(void)
 		writel(dram_vals[i], MXS_DRAM_BASE + (4 * i));
 
 #ifdef CONFIG_MX23
+	/*
+	 * Enable tRAS lockout in HW_DRAM_CTL08 ; it must be the last
+	 * element to be set
+	 */
 	writel((1 << 24), MXS_DRAM_BASE + (4 * 8));
 #endif
 }