ASoC: fsl_rpmsg: Allocate a smaller buffer size for capture stream

ASoC: fsl_rpmsg: Allocate a smaller buffer size for capture stream

If both playback and capture streams have large buffer size in low power
audio case, the total size will exceed the maximum buffer size for this
sound card.

Capture stream doesn't need so large buffer size in fact. So calculate
a reasonable smaller buffer size and allocate it for capture stream.

Signed-off-by: Chancel Liu <chancel.liu@nxp.com>
Link: https://patch.msgid.link/20250421105701.2273588-2-chancel.liu@nxp.com
Signed-off-by: Mark Brown <broonie@kernel.org>