The unsigned long datatype is not sufficient for mapping physical addresses
>= 4GB.

This patch ensures that the phys_addr_t datatype is used to represent physical
addresses when converting from a PFN.

Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>