drm/amd/display: Add DC build_id to determine build type

[why]
Sometimes there are indications that the incorrect driver is being
loaded in automated tests. This change adds the ability for builds to
be tagged with a string, and picked up by the test infrastructure.

[how]
dc.c will allocate const for build id, which is init-ed with default
value, indicating production build. For test builds, build server will
find/replace this value. The test machine will then verify this value.

Signed-off-by: Jun Lei <Jun.Lei@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>