package/freescale-imx: add option for i.MX8

package/freescale-imx: add option for i.MX8

The i.MX8 family has both the i.MX8QP and i.MX8QM.

See [0] for an overall presentation of all i.MX8 series, and [1] for
i.MX8 itself, which includes i.MX8QM (i.MX8 Quad Max) and i.MX8QP
(i.MX8 Quad Plus), which both have a quad Cortex-A53, the Plus has a
single Cortex-A72 and the Max has a dual Cortex-A72.

[0] https://www.nxp.com/products/processors-and-microcontrollers/arm-processors/i.mx-applications-processors/i.mx-8-processors:IMX8-SERIES
[1] https://www.nxp.com/products/processors-and-microcontrollers/arm-processors/i.mx-applications-processors/i.mx-8-processors/i.mx-8-family-arm-cortex-a53-cortex-a72-virtualization-vision-3d-graphics-4k-video:i.MX8

Signed-off-by: Maeva Manuel <maeva.manuel@nxp.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>