anv: Implement vkCmdDispatchBase

This is part of the device groups extension/feature but it's a decent
chunk of work in its own right so it's worth breaking into its own
patch.  The mechanism we use is fairly straightforward: we just push the
base work group id into the shader and add it to the work group id we
get from dispatch.

Reviewed-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com>

src/intel/compiler/brw_compiler.h

@@ -551,6 +551,9 @@ enum brw_param_builtin {
    BRW_PARAM_BUILTIN_TESS_LEVEL_INNER_X,
    BRW_PARAM_BUILTIN_TESS_LEVEL_INNER_Y,
 
+   BRW_PARAM_BUILTIN_BASE_WORK_GROUP_ID_X,
+   BRW_PARAM_BUILTIN_BASE_WORK_GROUP_ID_Y,
+   BRW_PARAM_BUILTIN_BASE_WORK_GROUP_ID_Z,
    BRW_PARAM_BUILTIN_SUBGROUP_ID,
 };