drm/tests: helpers: Add atomic helpers

drm/tests: helpers: Add atomic helpers

[ Upstream commit 66671944e17644804cb0886489e1b8fde924e9b9 ]

The mock device we were creating was missing any of the driver-wide
helpers. That was fine before since we weren't testing the atomic state
path, but we're going to start, so let's use the default
implementations.

Reviewed-by: Maíra Canal <mcanal@igalia.com>
Signed-off-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240222-kms-hdmi-connector-state-v7-2-8f4af575fce2@kernel.org
Stable-dep-of: 70f29ca3117a ("drm/tests: cmdline: Fix drm_display_mode memory leak")
Signed-off-by: Sasha Levin <sashal@kernel.org>