pl111: Rename the pl111 driver to "kmsro".

The vc4 driver can do prime sharing to many different KMS-only devices,
such as the various tinydrm drivers for SPI-attached displays.  Rename the
driver away from "pl111" to represent what it will actually support:
various sorts of KMS displays with the renderonly layer used to attach a
GPU.

Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Acked-by: Emil Velikov <emil.velikov@collabora.com>

meson_options.txt

@@ -58,7 +58,7 @@ option(
   type : 'array',
   value : ['auto'],
   choices : [
-    '', 'auto', 'pl111', 'radeonsi', 'r300', 'r600', 'nouveau', 'freedreno',
+    '', 'auto', 'kmsro', 'radeonsi', 'r300', 'r600', 'nouveau', 'freedreno',
     'swrast', 'v3d', 'vc4', 'etnaviv', 'imx', 'tegra', 'i915', 'svga', 'virgl',
     'swr',
   ],