We will remove the current assumption that the primary plane has the
same size and position as CRTC and that the primary plane is the
bottom-most in zpos order, or is even enabled. At least as far
as the blending machinery is concerned.

For that we will add CRTC dimension information to `vkms_crtc_state`
and add a opaque black backgound color.

Because now we need to fill the background, we had a loss in
performance with this change. Results running the IGT[1] test
`igt@kms_cursor_crc@pipe-a-cursor-512x512-onscreen` ten times:

|                  Frametime                   |
|:--------------------------------------------:|
|  Implementation |  Previous |   This commit  |
|:---------------:|:---------:|:--------------:|
| frametime range |  5~18 ms  |     10~22 ms   |
|     Average     |  8.47 ms  |     12.32 ms   |

[1] IGT commit id: bc3f6833a12221a46659535dac06ebb312490eb4

V6: Improve the commit description (Pekka Paalanen).
    Update some comments (Pekka Paalanen).
    Remove some fields from `vkms_crtc_state` and move where
    some variables are set (Pekka Paalanen).
Reviewed-by: Melissa Wen <mwen@igalia.com>
Signed-off-by: Igor Torrente <igormtorrente@gmail.com>
Signed-off-by: Melissa Wen <melissa.srw@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220905190811.25024-8-igormtorrente@gmail.com