wam: Require weston@display service

wam: Require weston@display service

WebAppMgr depends on weston@display.service

Bug-AGL: SPEC-3544

Signed-off-by: Antia Puentes <apuentes@igalia.com>
Change-Id: I5dc0980237a7a09306c7aec88b7dbeba807d2fcd
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl/+/25174
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: Scott Murray <scott.murray@konsulko.com>
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>