meson: Remove build_by_default from amd code

This is the same logic as the previous two patches.

Signed-off-by: Dylan Baker <dylanx.c.baker@intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
diff --git a/src/meson.build b/src/meson.build
index c3b1ff0..9232cc4 100644
--- a/src/meson.build
+++ b/src/meson.build
@@ -51,7 +51,9 @@
 subdir('compiler')
 subdir('egl/wayland/wayland-drm')
 subdir('vulkan')
-subdir('amd')
+if with_gallium_radeonsi or with_amd_vk
+  subdir('amd')
+endif
 if with_gallium_vc4
   subdir('broadcom')
 endif