mm/cma.c: export functions to be called from DLKM driver

export cma_get_base/cma_get_size for audio drivers
to allocate cma buffer.

Change-Id: Ib5e28981a598b4981331ef152f248220d9c2d051
Signed-off-by: Asish Bhattacharya <asishb@codeaurora.org>