meson: bump required libdrm version to 2.4.81
dbb4457d 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: dbb4457d ("egl: add EGL_EXT_device_drm support")
Cc: @evelikov