sysbench memory test

[LMM]

I updated the kernel with the mainline kernel (5.0), and the performance seems really better for the rockpro64 :
- for CPU 0-3 : 2163 MiB/s
- for CPU 4 and 5 : 6760 MiB/s

Note that in this test, I used a block of 1M, this is rather big.