thunderbolt: Optimize NHI LC mailbox command processing

thunderbolt: Optimize NHI LC mailbox command processing

Currently the Ice Lake and Tiger Lake NHI (host controller) LC (link
controller) mailbox command processing checks for the completion of
command every 100 msecs. These controllers are found to complete this in
the order of 1 ms or so. Since this delay is in suspend path, surplus
delay is effectively affecting runtime PM suspend flows.

Optimize this so that we do the wait for 1 ms after reading the mailbox
register. This should make Ice Lake and Tiger Lake runtime suspend take
less time to complete.

Reported-by: Dana Alkattan <dana.alkattan@intel.com>
Signed-off-by: Rajmohan Mani <rajmohan.mani@intel.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>