drm: meson: venc: cvbs: fix CVBS mode matching

With commit 222ec161 ("drm: Add aspect ratio parsing in DRM
layer") the drm core started honoring the picture_aspect_ratio field
when comparing two drm_display_modes. Prior to that it was ignored.
When the CVBS encoder driver was initially submitted there was no aspect
ratio check.

Switch from drm_mode_equal() to drm_mode_match() without
DRM_MODE_MATCH_ASPECT_RATIO to fix "kmscube" and X.org output using the
CVBS connector. When (for example) kmscube sets the output mode when
using the CVBS connector it passes HDMI_PICTURE_ASPECT_NONE, making the
drm_mode_equal() fail as it include the aspect ratio.

Prior to this patch kmscube reported:
  failed to set mode: Invalid argument

The CVBS mode checking in the sun4i (drivers/gpu/drm/sun4i/sun4i_tv.c
sun4i_tv_mode_to_drm_mode) and ZTE (drivers/gpu/drm/zte/zx_tvenc.c
tvenc_mode_{pal,ntsc}) drivers don't set the "picture_aspect_ratio" at
all. The Meson VPU driver does not rely on the aspect ratio for the CVBS
output so we can safely decouple it from the hdmi_picture_aspect
setting.

Cc: <stable@vger.kernel.org>
Fixes: 222ec161 ("drm: Add aspect ratio parsing in DRM layer")
Fixes: bbbe775e ("drm: Add support for Amlogic Meson Graphic Controller")
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Acked-by: Neil Armstrong <narmstrong@baylibre.com>
[narmstrong: squashed with drm: meson: venc: cvbs: deduplicate the meson_cvbs_mode lookup code]
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191208171832.1064772-3-martin.blumenstingl@googlemail.com