flutter-ics-homescreen: disable bg animation

flutter-ics-homescreen: disable bg animation

For now, disable the background animation on all platforms except
M3/H3 by passing the build time environment flag.  This will be
revisited to work out a runtime configuration scheme after the
Quillback M1 release.

Bug-AGL: SPEC-4984

Change-Id: I4938b0bb46fd04e36f4a006fb1fb4cef7f565896
Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl-demo/+/29473
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>
ci-image-build: Jenkins Job builder account
ci-image-boot-test: Jenkins Job builder account
Tested-by: Jenkins Job builder account