drm/fourcc: Add missing half-float formats

Not something that is likely to be scanned out, but GPUs usually support
half-float formats with 1, 2, or possibly 3 components, and it is useful
to be able to import/export them with a valid fourcc, and/or use gbm to
create them.

These correspond to PIPE_FORMAT_{R16,R16G16,R16G16B16}_FLOAT in mesa.

Signed-off-by: Rob Clark <robin.clark@oss.qualcomm.com>
Acked-by: Simona Vetter <simona@ffwll.ch>
Acked-by: Daniel Stone <daniels@collabora.com>
Link: https://lore.kernel.org/r/20250625173712.116446-2-robin.clark@oss.qualcomm.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>

Author: Rob Clark

include/uapi/drm/drm_fourcc.h

@@ -218,7 +218,7 @@ extern "C" {
 #define DRM_FORMAT_ABGR16161616	fourcc_code('A', 'B', '4', '8') /* [63:0] A:B:G:R 16:16:16:16 little endian */
 
 /*
- * Floating point 64bpp RGB
+ * Half-Floating point - 16b/component
  * IEEE 754-2008 binary16 half-precision float
  * [15:0] sign:exponent:mantissa 1:5:10
  */
@@ -228,6 +228,10 @@ extern "C" {
 #define DRM_FORMAT_ARGB16161616F fourcc_code('A', 'R', '4', 'H') /* [63:0] A:R:G:B 16:16:16:16 little endian */
 #define DRM_FORMAT_ABGR16161616F fourcc_code('A', 'B', '4', 'H') /* [63:0] A:B:G:R 16:16:16:16 little endian */
 
+#define DRM_FORMAT_R16F          fourcc_code('R', ' ', ' ', 'H') /* [15:0] R 16 little endian */
+#define DRM_FORMAT_GR1616F       fourcc_code('G', 'R', ' ', 'H') /* [31:0] G:R 16:16 little endian */
+#define DRM_FORMAT_BGR161616F    fourcc_code('B', 'G', 'R', 'H') /* [47:0] B:G:R 16:16:16 little endian */
+
 /*
  * RGBA format with 10-bit components packed in 64-bit per pixel, with 6 bits
  * of unused padding per component: