dwc3-msm: Log link TRB address and also readback ring doorbell register

In some cases, it has been observed that USB GSI wrapper is trying to
use possibly stale link trb address causing unmapped SMMU page fault.
Hence to confirm this observation log link trb address used for ringing
doorbell as well readback doorbell register to make sure writes are
flushed (i.e. not buffered at cache or bus level).

Change-Id: Ib833f432012738e8424d45c84091cd181c6e4a81
Signed-off-by: Mayank Rana <mrana@codeaurora.org>
Signed-off-by: Ajay Agarwal <ajaya@codeaurora.org>