asahi: Add and support the no_fp16 driconf flag

This is the driconf equivalent of our debug no16 flag, which disables
fp16 support to work around apps using bad GLSL precision qualifiers.

Signed-off-by: Asahi Lina <lina@asahilina.net>
Reviewed-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Eric Engestrom <eric@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25052>

src/util/driconf.h

@@ -465,6 +465,10 @@
    DRI_CONF_OPT_B(allow_multisampled_copyteximage, def, \
                   "Allow CopyTexSubImage and other to copy sampled framebuffer")
 
+#define DRI_CONF_NO_FP16(def) \
+   DRI_CONF_OPT_B(no_fp16, def, \
+                  "Disable 16-bit float support")
+
 /**
  * \brief Initialization configuration options
  */