xhci: Convert xhci_handshake() to use readl_poll_timeout_atomic()

xhci: Convert xhci_handshake() to use readl_poll_timeout_atomic()

Xhci_handshake() implements the algorithm already captured by
readl_poll_timeout_atomic(). Convert the former to use the latter to
avoid repetition.

Turned out this patch also fixes a bug on the AMD Stoneyridge platform
where usleep(1) sometimes takes over 10ms.
This means a 5 second timeout can easily take over 15 seconds which will
trigger the watchdog and reboot the system.

[Add info about patch fixing a bug to commit message -Mathias]
Signed-off-by: Andrey Smirnov <[email protected]>
Tested-by: Raul E Rangel <[email protected]>
Reviewed-by: Raul E Rangel <[email protected]>
Cc: <[email protected]>
Signed-off-by: Mathias Nyman <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>