i.MX28: Add function to adjust memory parameters

This function can be overridden at run-time and allows implementors
of new boards based on the i.MX28 chip to fine-tune the memory params.
It is possible to write into the dram_vals array because when the SPL
runs, it is located SRAM. Therefore the location is writable. There is
no possibility of these data to be read-only.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Wolfgang Denk <wd@denx.de>
Cc: Detlev Zundel <dzu@denx.de>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Fabio Estevam <festevam@gmail.com>

arch/arm/cpu/arm926ejs/mx28/spl_mem_init.c

@@ -82,10 +82,18 @@ uint32_t dram_vals[] = {
 	0x00000000, 0x00010001
 };
 
+void __mx28_adjust_memory_params(uint32_t *dram_vals)
+{
+}
+void mx28_adjust_memory_params(uint32_t *dram_vals)
+	__attribute__((weak, alias("__mx28_adjust_memory_params")));
+
 void init_m28_200mhz_ddr2(void)
 {
 	int i;
 
+	mx28_adjust_memory_params(dram_vals);
+
 	for (i = 0; i < ARRAY_SIZE(dram_vals); i++)
 		writel(dram_vals[i], MXS_DRAM_BASE + (4 * i));
 }