mm: fix lowmem issue

mm: fix lowmem issue

PD#157252: mm: fix lowmem issue

1. add statistics for CMA pages;
2. reduce cma print and not protect cma unless driver called;
3. fix cma usage policy in alloc path;
4. increase file scan ratio in kswapd;
5. using NOOP for default IO-scheduler;
6. change alloc flags of ZRAM to retry harder.

Change-Id: If7b0363da03da1682efe3996c69bb9d511299209
Signed-off-by: tao zeng <tao.zeng@amlogic.com>