ASoC: wm_adsp: Rename memory fields in wm_adsp_buffer

The wm_adsp_buffer struct is the control header of a circular
buffer used to transfer data from the firmware over the
control interface to an ALSA compressed stream.

The original names of the fields pointing to the data buffer
were based on ADSP2V2 memory layout where they correspond to
{XM, XM, YM}. But this circular buffer could be used on other
types of DSP core that have different memory region types.
Also the names and description of the size fields were not
very clear. The field names and descriptions have been changed
to be generic and not imply any particular memory types.

This patch updates the wm_adsp driver to the new field names.

Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Signed-off-by: Mark Brown <broonie@kernel.org>