util/format: make Y8_UNORM an alias of Y8_400_UNORM

The definiton of Y8_UNORM and Y8_400_UNORM are already identical, with
the only real difference being that pipe_format_to_chroma_format() does
not return R8 for Y8_UNORM. But Y8_UNORM is only used by freedreno,
the intel drivers and virgl, none of which doesn't even call
pipe_format_to_chroma_format() in the first place, so this shouldn't
matter.

Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Eric R. Smith <eric.smith@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/41151>

src/util/format/u_format.yaml

@@ -2033,6 +2033,7 @@
   channels: []
   swizzles: [X, Y, Z, W]
 - name: Y8_400_UNORM
+  alias: Y8_UNORM
   layout: other
   colorspace: YUV
   block: {width: 1, height: 1, depth: 1}
@@ -2183,15 +2184,6 @@
   channels: [X120]
   swizzles: [X, Y, Z, 1]
 
-# While most of Mesa uses R8 for Y, U, and V planes, freedreno requires
-# distinguishing between tiled Y8 data and tiled R8 data.
-- name: Y8_UNORM
-  layout: other
-  colorspace: YUV
-  block: {width: 1, height: 1, depth: 1}
-  channels: [UN8]
-  swizzles: [X, 0, 0, 1]
-
 # 10-bit channels stored in 16-bit containers (upper 10 bits used,
 # lower 6 bits are padding).
 - name: X6R10X6G10X6B10X6A10_UNORM

src/util/format/u_format_table.py

@@ -142,7 +142,6 @@ def has_access(format):
         'r8_g8_b8_444_unorm',
         'r8g8b8_420_unorm_packed',
         'r10g10b10_420_unorm_packed',
-        'y8_unorm',
         'y8u8v8_420_unorm_packed',
         'y10u10v10_420_unorm_packed',
         'g8_b8r8_444_unorm',
@@ -437,9 +436,6 @@ def write_get_plane_format(formats):
         'X4B12X4R12': 'X4R12X4G12',
     }
 
-    # On some YUV formats, we don't want RGB lowering
-    no_rgb_lowering = ['Y8_UNORM']
-
     print('static inline enum pipe_format', file=sys.stdout3)
     print('util_format_get_plane_format(enum pipe_format format, unsigned plane)', file=sys.stdout3)
     print('{', file=sys.stdout3)
@@ -449,10 +445,6 @@ def write_get_plane_format(formats):
         if f.layout not in ['planar2', 'planar3'] and f.colorspace != 'YUV':
             continue
 
-        if f.short_name().upper() in no_rgb_lowering:
-            unhandled_formats += [f.name]
-            continue
-
         nplanes = int(f.layout[-1]) if f.layout.startswith('planar') else 1
         planes = f.short_name().upper().split('_')
         if planes[-1] == 'PACKED':