xhci: plat: Register shutdown for xhci_plat

[ Upstream commit b07c12517f2aed0add8ce18146bb426b14099392 ]

Shutdown should be called for xhci_plat devices especially for
situations where kexec might be used by stopping DMA
transactions.

Signed-off-by: Adam Wallis <awallis@codeaurora.org>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>