ARM: update __swp_entry_to_pte() to use PTE_TYPE_FAULT

Swap entries use a faulting PTE which have the least two significant
bits as zero. Due to this, the use of PTE_TYPE_FAULT was overlooked,
but really should have been included in __swp_entry_to_pte().

Convert this macro to use PTE_TYPE_FAULT to properly document what is
going on here, and use __pte() to convert the swp_entry_t to a pte_t.

This results in no change to the resulting kernel image.

Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>