slimbus: ngd: Rely on HW status for capability negotiation message

HW status in config register will provide consistent information
in case HW status changes due to unexpected noise on the lines.
Use that status to initiate capability negotiation rather than
SW status.
This means the negotiation may take place during runtime if HW
experiences noise. Ensure completion objects don't get re-initialized
accidentally due to this since thread responsible for exchanging this
capability can be waiting on it.

Change-Id: Ifee39473b7b4b63de44a392bb4040bcd9b98e2ff
Signed-off-by: Sagar Dharia <sdharia@codeaurora.org>