drm/tests: Add helper to create mock crtc

drm/tests: Add helper to create mock crtc

[ Upstream commit 51f90720381dea79208513d059e0eb426dee511e ]

We're going to need a full-blown, functional, KMS device to test more
components of the atomic modesetting infrastructure.

Let's add a new helper to create a dumb, mocked, CRTC. By default it
will create a CRTC relying only on the default helpers, but drivers are
free to deviate from that.

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-v7-4-8f4af575fce2@kernel.org
Stable-dep-of: 70f29ca3117a ("drm/tests: cmdline: Fix drm_display_mode memory leak")
Signed-off-by: Sasha Levin <sashal@kernel.org>