i965_drv_video: Bump the libdrm dependency to 2.4.23 for I915_EXEC_BLT

I915_EXEC_BLT has landed recently-ish in libdrm and you need v2.4.23 to
be able to compile the i965 driver.
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>

configure.ac

@@ -104,9 +104,9 @@ PKG_CHECK_MODULES([DRM], [libdrm])
 PKG_CHECK_MODULES(GEN4ASM, [intel-gen4asm >= 1.1], [gen4asm=yes], [gen4asm=no])
 AM_CONDITIONAL(HAVE_GEN4ASM, test x$gen4asm = xyes)
 
-# Check for libdrm >= 2.4.21 (needed for i965_drv_video.so)
-if test x$enable_i965_driver = xyes && ! $PKG_CONFIG --atleast-version=2.4.21 libdrm; then
-    AC_MSG_WARN([libdrm < 2.4.21 found, disabling build of i965 video driver])
+# Check for libdrm >= 2.4.23 (needed for i965_drv_video.so)
+if test x$enable_i965_driver = xyes && ! $PKG_CONFIG --atleast-version=2.4.23 libdrm; then
+    AC_MSG_WARN([libdrm < 2.4.23 found, disabling build of i965 video driver])
     enable_i965_driver=no
 fi
 AM_CONDITIONAL(BUILD_I965_DRIVER, test x$enable_i965_driver = xyes)