meson: Add support for the pl111 driver.

Reviewed-by: Dylan Baker <dylan@pnwbakers.com>
diff --git a/meson_options.txt b/meson_options.txt
index 51a1805..8fd00d4 100644
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -46,7 +46,7 @@
 option(
   'gallium-drivers',
   type : 'string',
-  value : 'radeonsi,nouveau,swrast,vc4',
+  value : 'pl111,radeonsi,nouveau,swrast,vc4',
   description : 'comma separated list of gallium drivers to build.'
 )
 option(