soc: xtensa: adsp: add support for NXP ADSP

Add a common part for all i.MX boards.

Add support for i.MX8, which represents i.MX8QM.
This has a 1 Xtensa HiFi4 core, with 64 KB TCM,
448 KB OCRAM, 8MB SDRAM and 1 ESAI, 1 SAI as
audio interfaces.

Signed-off-by: Iuliana Prodan <iuliana.prodan@nxp.com>