interconnect: Add debugfs test code

Allow setting constraints from userspace for more convenient testing.

Example usage:
	cd /sys/kernel/debug/interconnect-test/
	echo -n 3 > src_port
	echo -n 53 > dst_port
	echo -n 1 > get
	echo -n 80000000 > avg_bw
	echo -n 90000000 > peak_bw
	echo -n 1 > commit

Change-Id: I8a47c45a8060607470edc870b1eb4245bb7ffc54
Signed-off-by: Georgi Djakov <georgi.djakov@linaro.org>
Signed-off-by: David Dai <daidavid1@codeaurora.org>
Git-commit: 8b9e75c3e826f6a719ff02fa409f6b9c92aee66c
Git-repo: https://git.linaro.org/people/georgi.djakov/linux.git


Signed-off-by: Georgi Djakov <gdjako@codeaurora.org>