asoc: wcd-spi: use CMA memory for TX and RX buffer instead of kzalloc

In wcd-spi driver, the kzalloc is used to allocate memory for TX and
RX buffer. Those allocations are order4 or order5, which could fail
on some kernels. To avoid potential memory allocation failure, the CMA
region is used for those allocations by dma_alloc_coherent API.

Change-Id: I0a4d6c6b5e0e47f96187563272e63c3a006e469f
Signed-off-by: Xiaoyu Ye <benyxy@codeaurora.org>