add documentation for imx8 boards

Toradex Apalis iMX8

• https://www.toradex.com/computer-on-modules/apalis-arm-family/nxp-imx-8
• supports only v1.0B silicon
  Toradex Colibri iMX8QXP
• https://www.toradex.com/computer-on-modules/colibri-arm-family/nxp-imx-8x
• supports only v1.0B silicon

Both toradex boards are flashed with same instructions as WaRP7

NXP i.MX 8MQuad EVK
https://www.nxp.com/support/developer-resources/evaluation-and-development-boards/i.mx-evaluation-and-development-boards/evaluation-kit-for-the-i.mx-8m-applications-processor:MCIMX8M-EVK

NXP i.MX 8QuadMax MEK
https://www.nxp.com/support/developer-resources/evaluation-and-development-boards/i.mx-evaluation-and-development-boards/i.mx-8quadmax-multisensory-enablement-kit-mek:MCIMX8QM-CPU

both NXP boards are flashing normally to a SD card