size_t is the canonical type to represent variables that contain a size.
Use it instead of signed integer. Physical addresses can be larger than
32-bit, so use a more appropriate type for them as well. phys_addr_t is
a type that is 32-bit on systems that use 32-bit addresses and 64-bit if
the system is 64-bit or uses a form of physical address extension to use
a larger address space on 32-bit systems. Using these types the same API
can be implemented on a wider range of systems.

Signed-off-by: Thierry Reding <treding@nvidia.com>