ntb_hw_switchtec: Fix setup MW with failure bug

Switchtec does not support setting multiple MWs simultaneously. The
driver takes a hardware lock to ensure that two peers are not doing this
simultaneously and it fails if someone else takes the lock. In most
cases, this is fine as clients only setup the MWs once on one side of
the link.

However, there's a race condition when a re-initialization is caused by
a link event. The driver will re-setup the shared memory window
asynchronously and this races with the client setting up it's memory
windows on the link up event.

To fix this we ensure do the entire initialization in a work queue and
signal the client once it's done.

Signed-off-by: Joey Zhang <joey.zhang@microchip.com>
Signed-off-by: Wesley Sheng <wesley.sheng@microchip.com>
Signed-off-by: Jon Mason <jdmason@kudzu.us>