revert: "gpu: don't hard error on invalid drm format modifiers"

This reverts commit c238c51.

Turns out that we actually need this check in order to prevent mpv from
accidentally choosing hwdec=vaapi instead of hwdec=vaapi-copy on older
drivers that don't support DRM modifiers, at the very least.

In general, the lesson learned is that we _really_ shouldn't allow
passing invalid DRM format modifiers. Users need to get this right to
use the API. That's simply the way it is.

Fixes #98
Fixes mpv-player/mpv#8702
See also mpv-player/mpv#8668

src/gpu.c

@@ -530,29 +530,20 @@ pl_fmt pl_find_fourcc(pl_gpu gpu, uint32_t fourcc)
     return NULL;
 }
 
-static bool warned_mods = false;
-
-static inline void check_mod(pl_gpu gpu, pl_fmt fmt, uint64_t mod)
+static inline bool check_mod(pl_gpu gpu, pl_fmt fmt, uint64_t mod)
 {
-    if (warned_mods)
-        return;
-
     for (int i = 0; i < fmt->num_modifiers; i++) {
         if (fmt->modifiers[i] == mod)
-            return;
+            return true;
     }
 
-    // This is not a hard error because modifier support is fickle at best,
-    // in both libplacebo and other APIs. So just be somewhat annoying in this
-    // case.
 
-    PL_WARN(gpu, "DRM modifier %s not available for format %s. Ignoring, "
-            "but expect possible corruption. Available modifiers:",
-            PRINT_DRM_MOD(mod), fmt->name);
+    PL_ERR(gpu, "DRM modifier %s not available for format %s. Available modifiers:",
+           PRINT_DRM_MOD(mod), fmt->name);
     for (int i = 0; i < fmt->num_modifiers; i++)
-        PL_WARN(gpu, "    %s", PRINT_DRM_MOD(fmt->modifiers[i]));
+        PL_ERR(gpu, "    %s", PRINT_DRM_MOD(fmt->modifiers[i]));
 
-    warned_mods = true;
+    return false;
 }
 
 pl_tex pl_tex_create(pl_gpu gpu, const struct pl_tex_params *params)
@@ -568,7 +559,8 @@ pl_tex pl_tex_create(pl_gpu gpu, const struct pl_tex_params *params)
         require(PL_ISPOT(params->import_handle));
         require(params->shared_mem.size > 0);
         if (params->import_handle == PL_HANDLE_DMA_BUF) {
-            check_mod(gpu, params->format, params->shared_mem.drm_format_mod);
+            if (!check_mod(gpu, params->format, params->shared_mem.drm_format_mod))
+                goto error;
             if (params->shared_mem.stride_w)
                 require(params->w && params->shared_mem.stride_w >= params->w);
             if (params->shared_mem.stride_h)