meta-agl-profile-graphical: add device dependency hook in weston-init

meta-agl-profile-graphical: add device dependency hook in weston-init

Add a mechanism in the weston-init recipe to allow machine templates
to trigger installation of a systemd drop-in that adds a DRM device
dependency for the weston@.service unit.  Also, tweak the qemux86-64
configuration to enable doing so against dev-dri-card0.device to avoid
startup failures due to the slow i915 initialization on e.g. the
UpSquared.  This approach has been taken since it seems safer for now
to only apply it for qemux86-64 than doing a blanket default that
might then need to be over-ridden for vendor BSPs.

Bug-AGL: SPEC-3518

Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Change-Id: I74ce4f878f9aa3f0d555f96a79578f3d8ca72550
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl/+/25688
ci-image-build: Jenkins Job builder account <agl-jobbuilder@automotivelinux.org>
Tested-by: Jenkins Job builder account <agl-jobbuilder@automotivelinux.org>
ci-image-boot-test: Jenkins Job builder account <agl-jobbuilder@automotivelinux.org>
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>