drm: vkms: Supports to the case where primary plane doesn't match the CRTC

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