[U-Boot] [PATCH 1/3 v2] 83xx: Default to using DMA to initializeSDRAM

[Liu Dave-R63238]

> According to Ira, the DMA method was faster than the cpu method:
> "It makes the DMA initialization normal speed again. The DMA 
> in the for loop takes the longest (as expected).
> 
> So yes, strangely it (enabling the icache) makes a HUGE 
> difference. The total time is <3 seconds now. It is now 
> faster than the previous CPU method."
> 
> 
> Logically the DMA method should be faster, and Ira's results 
> seem to reinforce this.  I don't have an 83xx board to test 
> on, so let me know if others have different results than Ira.

I did the DMA init test with the orignal DMA code. At that time
The DMA method is slower than CPU method. Strange why the
result is different.

Not sure what is the new DMA code?

DMA method needs read and write bus transaction, but CPU doesn't
need the read transaction. Alougth the DMA may be burst read/write.

Anyway, the test result determine all.