autoconf/scons: bump libdrm to 2.4.75

We'll be using the drmGetDevice[s]2 API in src/loader with next patch.

v2: Rebase.

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Michel Dänzer <michel.daenzer@amd.com> (v1)
Reviewed-by: Eric Engestrom <eric.engestrom@imgtec.com> (v1)
Tested-by: Mike Lothian <mike@fireburn.co.uk>
diff --git a/configure.ac b/configure.ac
index 1d81fcc..6b65ff8 100644
--- a/configure.ac
+++ b/configure.ac
@@ -72,7 +72,7 @@
 # codifies which drivers need which version of libdrm. Any libdrm
 # version dependencies in non-driver-specific code should be reflected
 # in the first entry.
-LIBDRM_REQUIRED=2.4.66
+LIBDRM_REQUIRED=2.4.75
 LIBDRM_RADEON_REQUIRED=2.4.71
 LIBDRM_AMDGPU_REQUIRED=2.4.63
 LIBDRM_INTEL_REQUIRED=2.4.75