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

include/drm/drm_fixed.h

@@ -71,6 +71,7 @@ static inline u32 dfixed_div(fixed20_12 A, fixed20_12 B)
 }
 
 #define DRM_FIXED_POINT		32
+#define DRM_FIXED_POINT_HALF	16
 #define DRM_FIXED_ONE		(1ULL << DRM_FIXED_POINT)
 #define DRM_FIXED_DECIMAL_MASK	(DRM_FIXED_ONE - 1)
 #define DRM_FIXED_DIGITS_MASK	(~DRM_FIXED_DECIMAL_MASK)
@@ -87,6 +88,11 @@ static inline int drm_fixp2int(s64 a)
 	return ((s64)a) >> DRM_FIXED_POINT;
 }
 
+static inline int drm_fixp2int_round(s64 a)
+{
+	return drm_fixp2int(a + (1 << (DRM_FIXED_POINT_HALF - 1)));
+}
+
 static inline int drm_fixp2int_ceil(s64 a)
 {
 	if (a > 0)