doc: imx: imxrt1170: Document imxrt1170-evk board

Add documentation for imxrt1170-evk.

Signed-off-by: Jesse Taube <Mr.Bossman075@gmail.com>
Reviewed-by: Giulio Benetti <giulio.benetti@benettiengineering.com>

Add index page entry, adjust formatting.
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>