configure.ac: bump LIBDRM_RADEON requirement to 2.4.71

Such that we can remove all the local fall-back definitions and use the
official UABI ones.

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
diff --git a/configure.ac b/configure.ac
index e4a5b48..c850cb0 100644
--- a/configure.ac
+++ b/configure.ac
@@ -73,7 +73,7 @@
 # version dependencies in non-driver-specific code should be reflected
 # in the first entry.
 LIBDRM_REQUIRED=2.4.66
-LIBDRM_RADEON_REQUIRED=2.4.56
+LIBDRM_RADEON_REQUIRED=2.4.71
 LIBDRM_AMDGPU_REQUIRED=2.4.63
 LIBDRM_INTEL_REQUIRED=2.4.75
 LIBDRM_NVVIEUX_REQUIRED=2.4.66