ASoC: SOF: imx: Add i.MX8M HW support

ASoC: SOF: imx: Add i.MX8M HW support

This adds skeleton support for the audio DSP hardware found on NXP i.MX8M
platform.

There is one notable difference between i.MX8M and i.MX8, which doesn't
allow us to reuse HW support from imx8.c file designed for i.MX8:

On i.MX8M resources (clocks, power, pinctrl, etc) are managed by the
Linux kernel while on i.MX8 resources are managed by a separate
System Controller Firmware. This makes the interface to those resources
completely different.

Signed-off-by: Daniel Baluta <daniel.baluta@nxp.com>
Link: https://lore.kernel.org/r/20200409071832.2039-4-daniel.baluta@oss.nxp.com
Signed-off-by: Mark Brown <broonie@kernel.org>