USB: xhci: Represent 64-bit addresses with one u64.

There are several xHCI data structures that use two 32-bit fields to
represent a 64-bit address.  Since some architectures don't support 64-bit
PCI writes, the fields need to be written in two 32-bit writes.  The xHCI
specification says that if a platform is incapable of generating 64-bit
writes, software must write the low 32-bits first, then the high 32-bits.
Hardware that supports 64-bit addressing will wait for the high 32-bit
write before reading the revised value, and hardware that only supports
32-bit writes will ignore the high 32-bit write.

Previous xHCI code represented 64-bit addresses with two u32 values.  This
lead to buggy code that would write the 32-bits in the wrong order, or
forget to write the upper 32-bits.  Change the two u32s to one u64 and
create a function call to write all 64-bit addresses in the proper order.
This new function could be modified in the future if all platforms support
64-bit writes.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>