MIPS: Support 36-bit iomem on 32-bit Au1x00

I believe these changes are needed on Alchemy SoCs in order to
use iomem above 4G with the usual platform_device machinery:

- Set CONFIG_ARCH_PHYS_ADDR_T_64BIT to make resource_size_t 64-bit.
- Increase IOMEM_RESOURCE_END so that platforms can register resources.

To: linux-mips@linux-mips.org
Patchwork: http://patchwork.linux-mips.org/patch/814/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>