USB: xhci depends on PCI.

While it looks like xhci was written with both PCI and non-PCI in mind,
apparently only the former has seen any testing. xhci-mem.o can be "fixed"
with a linux/dmapool.h include, but there are still parts of the code that
make use of struct pci_dev directly. So, at least more work is needed before
this can be turned on for non-PCI builds:

  CC      drivers/usb/host/xhci-mem.o
drivers/usb/host/xhci-mem.c: In function 'xhci_segment_alloc':
drivers/usb/host/xhci-mem.c:45: error: implicit declaration of function 'dma_pool_alloc'
drivers/usb/host/xhci-mem.c:45: warning: assignment makes pointer from integer without a cast
drivers/usb/host/xhci-mem.c: In function 'xhci_segment_free':
drivers/usb/host/xhci-mem.c:67: error: implicit declaration of function 'dma_pool_free'
drivers/usb/host/xhci-mem.c: In function 'xhci_alloc_virt_device':
drivers/usb/host/xhci-mem.c:239: warning: assignment makes pointer from integer without a cast
drivers/usb/host/xhci-mem.c:248: warning: assignment makes pointer from integer without a cast
drivers/usb/host/xhci-mem.c: In function 'xhci_mem_cleanup':
drivers/usb/host/xhci-mem.c:578: error: implicit declaration of function 'dma_pool_destroy'
drivers/usb/host/xhci-mem.c: In function 'xhci_mem_init':
drivers/usb/host/xhci-mem.c:657: error: implicit declaration of function 'dma_pool_create'
drivers/usb/host/xhci-mem.c:658: warning: assignment makes pointer from integer without a cast
drivers/usb/host/xhci-mem.c:663: warning: assignment makes pointer from integer without a cast
make[3]: *** [drivers/usb/host/xhci-mem.o] Error 1

  CC      drivers/usb/host/xhci-pci.o
drivers/usb/host/xhci-pci.c: In function 'xhci_pci_reinit':
drivers/usb/host/xhci-pci.c:39: error: implicit declaration of function 'pci_set_mwi'
drivers/usb/host/xhci-pci.c: At top level:
drivers/usb/host/xhci-pci.c:151: error: 'usb_hcd_pci_probe' undeclared here (not in a function)
drivers/usb/host/xhci-pci.c:152: error: 'usb_hcd_pci_remove' undeclared here (not in a function)
drivers/usb/host/xhci-pci.c:155: error: 'usb_hcd_pci_shutdown' undeclared here (not in a function)
drivers/usb/host/xhci-pci.c:159: warning: function declaration isn't a prototype
drivers/usb/host/xhci-pci.c:164: warning: function declaration isn't a prototype
make[3]: *** [drivers/usb/host/xhci-pci.o] Error 1

Cc: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>