drivers: dma-contiguous: remove cma regions from kmemleak scan

cma regions can be allocated for secure use cases where
the virtual mapping is removed. kmemleak scan can try to
scan through this mapping causing mmu faults. Hence free
cma regions from kmemleak scan.

Change-Id: I2cc66423ec9ec539905cc8d07bbc40fa43e695bd
Signed-off-by: Shiraz Hashim <shashim@codeaurora.org>
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>
Signed-off-by: Prasad Sodagudi <psodagud@codeaurora.org>