meson: bump required libdrm version to 2.4.81

meson: bump required libdrm version to 2.4.81

dbb4457d9858fa977246 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: dbb4457d9858fa977246 ("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>