dra7xx DDR test

DDR 测试也可以用memtester：用户空间可以覆盖
Perform Memtester From Kernel
From kernel, you can verify DDR by running memtester from kernel. The memtester utility from kernel is
used to check integrity and functionality of the DDR by performing various memory tests like address path
test, data path test, stuck addres/data tests, and so forth.
Syntax : memtester [-p PHYSADDR] [ITERATIONS]
root@dra7xx-evm# memtester 3500M
DDR 压力测试的目的是把左右的内存都测试一遍。