tu+meson: Re-work KMD selection

Now that turnip can support multiple kernel-mode drivers in a single
build, re-work the meson option to have a single list of KMDs, rather
than special options to enable kgsl for turnip or virtio for gallium.

It is temporarily a bit awkward as gallium does not yet support kgsl
and turnip does not yet support virtio.  But both of those are planned
or in-progress, so long term a single list is the most sensible option.

TODO freedreno/drm support to build with only virtio support.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/21394>

meson_options.txt

@@ -198,19 +198,16 @@ option(
                 'will be built'
 )
 
+# Note that currently turnip supports msm and kgsl, while the gallium driver
+# support msm and virtio.  This is a temporary situation with virtio support
+# for turnip and kgsl support for gallium planned/in-progress.
 option(
-  'freedreno-kgsl',
-  type : 'boolean',
-  value : false,
-  description : 'use kgsl backend for freedreno vulkan driver',
-)
-
-option(
-  'freedreno-virtio',
-  type : 'boolean',
-  value : false,
-  description : 'use experimental virtio backend for freedreno (currently ' +
-                'only gallium driver)',
+  'freedreno-kmds',
+  type : 'array',
+  value : ['msm'],
+  choices : ['msm', 'kgsl', 'virtio'],
+  description : 'List of kernel-mode drivers to enable for freedreno ' +
+                'gallium and vulkan driver',
 )
 
 option(