meson: bump required libdrm version to 2.4.81

dbb4457d98 started using drmDevicesEqual(), which was
introduced in libdrm 2.4.81

We could either copy the function locally, or bump the required version.
Since the function is non-trivial and 2.4.81 is old enough already,
I suggesting the latter.

Fixes: dbb4457d98 ("egl: add EGL_EXT_device_drm support")
Cc: Emil Velikov <emil.velikov@collabora.com>
Signed-off-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-by: Dylan Baker <dylan@pnwbakers.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>

meson.build

@@ -1161,7 +1161,7 @@ _drm_amdgpu_ver = '2.4.97'
 _drm_radeon_ver = '2.4.71'
 _drm_nouveau_ver = '2.4.66'
 _drm_intel_ver = '2.4.75'
-_drm_ver = '2.4.75'
+_drm_ver = '2.4.81'
 
 _libdrm_checks = [
   ['intel', with_dri_i915 or with_gallium_i915],