interconnect: icc-rpm: Set destination bandwidth as well as source bandwidth

Make it possible to set destination as well as source bandwidth. If the
*dst pointer is non-NULL. Right now it appears that we never make the
destination bw allocation call, which is inconsistent with the downstream
way of doing this.

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>