Currently, The fixed 512KB prealloc buffer size is too larger for
tiny memory kernel (such as 16MB memory). This patch adds the module
option "prealloc_buffer_size_kbytes" to specify prealloc buffer size.

It's suitable for cards which use the generic dmaengine pcm driver
with no config.
Signed-off-by: Sugar Zhang <sugar.zhang@rock-chips.com>
Link: https://lore.kernel.org/r/1632394246-59341-1-git-send-email-sugar.zhang@rock-chips.comSigned-off-by: Mark Brown <broonie@kernel.org>