libdrm: Android.mk: Add minimal Android platform check

Add a check to error out on Android version K(4.4) or
lower.

This is due to dependency added in a previous commit on mmap64,
which was introduced with Android L.

Cc: Sean Paul <seanpaul@chromium.org>
Cc: Alistair Strachan <astrachan@google.com>
Cc: Marissa Wall <marissaw@google.com>
Suggested-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>