ASoC: xilinx: xlnx_i2s: create drvdata structure

An upcoming change will require storing additional driver data other
than the memory base address. Create a drvdata structure and use that
rather than storing the raw base address pointer.

Signed-off-by: Robert Hancock <robert.hancock@calian.com>
Link: https://lore.kernel.org/r/20220120195832.1742271-3-robert.hancock@calian.com


Signed-off-by: Mark Brown <broonie@kernel.org>