drm/atomic-helper: Don't allocate new plane state in CRTC check

In drm_atomic_helper_check_crtc_state(), do not add a new plane state
to the global state if it does not exist already. Adding a new plane
state will result in overhead for the plane during the atomic-commit
step.

For the test in drm_atomic_helper_check_crtc_state() to succeed, it
is important that the CRTC has an enabled primary plane after the
commit. Simply testing the CRTC state's plane_mask for a primary plane
is sufficient.

Note that the helper still only tests for an attached primary plane.
Drivers have to ensure that the plane contains valid pixel information.

v5:
	* fix commit description (Javier)
v3:
	* test for a primary plane in plane_mask (Ville)
v2:
	* remove unnecessary test for plane->crtc (Ville)
	* inline drm_atomic_get_next_plane_state() (Ville)
	* acquire plane lock before accessing plane->state (Ville)

Signed-off-by: Thomas Zimmermann <[email protected]>
Reviewed-by: Javier Martinez Canillas <[email protected]>
Fixes: d6b9af1097fe ("drm/atomic-helper: Add helper drm_atomic_helper_check_crtc_state()")
Cc: Thomas Zimmermann <[email protected]>
Cc: Jocelyn Falempe <[email protected]>
Cc: Maarten Lankhorst <[email protected]>
Cc: Maxime Ripard <[email protected]>
Cc: David Airlie <[email protected]>
Cc: Daniel Vetter <[email protected]>
Cc: [email protected]
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

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