Add imx8mqevk machine that uses etnaviv

Add imx8mqevk machine that uses etnaviv

To enable debugging/development of the etnaviv driver against the
GC7000L GPU in the i.MX8MQ, add a "imx8mqevk" template that uses
etnaviv instead of Vivante.  Since there seem to be some issues
with respect to GPU hangs and resulting graphical corruption, the
existing "imx8mqevk-viv" template that uses Vivante has been
retained for now.

Bug-AGL: SPEC-3520

Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Change-Id: If5b84c6021994cce0f30410985b1ec4678e718ef
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl/+/25058
Tested-by: Jenkins Job builder account <agl-jobbuilder@automotivelinux.org>
ci-image-build: Jenkins Job builder account <agl-jobbuilder@automotivelinux.org>
ci-image-boot-test: Jenkins Job builder account <agl-jobbuilder@automotivelinux.org>
Reviewed-by: Walter Lozano <walter.lozano@collabora.com>
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>