Fix dependency issue with grpc in meta-agl-core

Fix dependency issue with grpc in meta-agl-core

grpc is not in the core layer but in meta-oe . Guard the dependency and only enable when
prerequisites are met.

Bug-AGL: SPEC-4707
Change-Id: I922a846108ca13d8e6d50e79c3003b0b32a002a7
Signed-off-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl/+/28509
Reviewed-by: Marius Vlad <marius.vlad@collabora.com>
Tested-by: Jenkins Job builder account
ci-image-build: Jenkins Job builder account
ci-image-boot-test: Jenkins Job builder account