drm: Fix drm.h uapi header for GNU/kFreeBSD

Like GNU/Linux, GNU/kFreeBSD's sys/types.h does not define the uintX_t
types, which differs from the BSDs' headers. Thus we should include
stdint.h to ensure we have all the required integer types.

Signed-off-by: James Clarke <jrtc27@jrtc27.com>
Signed-off-by: Eric Anholt <eric@anholt.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20190115150418.68080-1-jrtc27@jrtc27.com


Reviewed-by: Eric Anholt <eric@anholt.net>