agl-compositor_git: Enable loading waltham-transmitter-plugin

agl-compositor_git: Enable loading waltham-transmitter-plugin

The build system is able to determine if it can build support for
loading the plug-in when waltham depedency is satified. We add
that based on AGL_FEATURES.

Bug-AGL: SPEC-3601

Signed-off-by: Marius Vlad <marius.vlad@collabora.com>
Change-Id: Id7279fddc12c78472ae22a480626106a00ea30db
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl/+/25699
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: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>