drm: Add fixed-point helper to get rounded integer values

Create a new fixed-point helper to allow us to return the rounded value
of our fixed point value.

[v2]:
    * Create the function drm_fixp2int_round() (Melissa Wen).
[v3]:
    * Use drm_fixp2int() instead of shifting manually (Arthur Grillo).

Signed-off-by: Maíra Canal <mcanal@igalia.com>
Reviewed-by: Arthur Grillo <arthurgrillo@riseup.net>
Signed-off-by: Maíra Canal <mairacanal@riseup.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20230512104044.65034-1-mcanal@igalia.com