meson: rework intel-rt option to be a feature

This allows intel-rt to be turned on in cases where we're on x86_64 and
we're building anv, but otherwise default to off, while still giving
users the power to ignore those defaults if they want to.

Because of the use of `feature.disable_if` this bumps the Meson
requirement to 1.1. I can get rid of that, but it just makes for a lot
more code than using the helper methods

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27645>

meson_options.txt

@@ -651,12 +651,8 @@ option(
 
 option(
   'intel-rt',
-  type : 'combo',
+  type : 'feature',
   deprecated: {'true': 'enabled', 'false': 'disabled'},
-  value : 'disabled',
-  choices : [
-    'enabled', 'disabled',
-  ],
   description : 'Build Ray Tracing on supported hardware.'
 )