mm: add cma debug interafce [1/1]

mm: add cma debug interafce [1/1]

PD#GH-17

Problem:
sometimes cma allocation failed but it's hard to get
failed log and need recompile code.

Solution:
Add /proc/cma_debug to open cma debug message dynamic.
By default, no debug message is printed. If you write a
value large than 0 to this node, debug message will be
printed.

Verify:
p212

Change-Id: Ibcfd1d48be5f33f674f09df713dc2e493748c405
Signed-off-by: tao zeng <tao.zeng@amlogic.com>