ion: update idr to avoid deprecated apis

Use idr_alloc instead if idr_pre_get/idr_get_new_above, and
remove idr_remove_all.

Signed-off-by: Colin Cross <ccross@android.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>