xhci: Fix DIV_ROUND_UP compile error.

Fengguang reports that the xHCI driver isn't linked properly on his
machine:

ERROR: "__udivdi3" [drivers/usb/host/xhci-hcd.ko] undefined!
ERROR: "handle_edge_irq" [drivers/gpio/gpio-pch.ko] undefined!
ERROR: "irq_to_desc" [drivers/gpio/gpio-pch.ko] undefined!

The driver compiles fine on my 64-bit box (gcc version 4.6.1).
Fengguang thinks it's because the xHCI driver was using DIV_ROUND_UP()
instead of DIV_ROUND_UP_ULL() with arguments that were unsigned long
long variables.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Reported-by: Wu Fengguang <wfg@linux.intel.com>