crypto: crypto4xx - reduce memory fragmentation

With recent kernels (>5.2), the driver fails to probe, as the
allocation of the driver's scatter buffer fails with -ENOMEM.

This happens in crypto4xx_build_sdr(). Where the driver tries
to get 512KiB (=PPC4XX_SD_BUFFER_SIZE * PPC4XX_NUM_SD) of
continuous memory. This big chunk is by design, since the driver
uses this circumstance in the crypto4xx_copy_pkt_to_dst() to
its advantage:
"all scatter-buffers are all neatly organized in one big
continuous ringbuffer; So scatterwalk_map_and_copy() can be
instructed to copy a range of buffers in one go."

The PowerPC arch does not have support for DMA_CMA. Hence,
this patch reorganizes the order in which the memory
allocations are done. Since the driver itself is responsible
for some of the issues.

Signed-off-by: Christian Lamparter <chunkeey@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>