ASoC: fsl: fsl_qmc_audio: Split channel buffer and PCM pointer handling

ASoC: fsl: fsl_qmc_audio: Split channel buffer and PCM pointer handling

The driver mixes some internal values for channel DMA buffer handling
and PCM pointer handling. In the currently supported interleaved mode,
this mix does not lead to any issues but in order to prepare the
support for the non-interleaved mode, having them clearly separated will
ease the support and avoid additional computation to convert values used
in channel DMA buffer management in values usable for PCM pointer.

Use a specific set of variable for PCM pointer handling and an other set
for channel DMA buffer.

Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Link: https://patch.msgid.link/20240701113038.55144-4-herve.codina@bootlin.com
Signed-off-by: Mark Brown <broonie@kernel.org>