uio: support memory sizes larger than 32 bits

This is a completion to 27a90700
The size field is also increased to allow values larger than 32 bits
on platforms that have more than 32 bit physical addresses.

Signed-off-by: Cristian Stoica <cristian.stoica@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>