imx: add i.MX8MQ SoC Revision and is_mx8m helper

Add i.MX8MQ SoC Revision
Add is_mx8m helper
The 7ULP is a dummy number, so use 0xEx.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Cc: Stefano Babic <sbabic@denx.de>
Reviewed-by: Stefano Babic <sbabic@denx.de>