usb: host: xhci-rcar: Fix timeout in xhci_suspend()

usb: host: xhci-rcar: Fix timeout in xhci_suspend()

When a USB device is connected to the host controller and
the system enters suspend, the following error happens
in xhci_suspend():

	xhci-hcd ee000000.usb: WARN: xHC CMD_RUN timeout

Since the firmware/internal CPU control the USBSTS.STS_HALT
and the process speed is down when the roothub port enters U3,
long delay for the handshake of STS_HALT is neeed in xhci_suspend().
So, this patch adds to set the XHCI_SLOW_SUSPEND.

Fixes: 435cc1138ec9 ("usb: host: xhci-plat: set resume_quirk() for R-Car controllers")
Cc: <stable@vger.kernel.org> # v4.12+
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Link: https://lore.kernel.org/r/1564734815-17964-1-git-send-email-yoshihiro.shimoda.uh@renesas.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>