parisc: Call pagefault_disable/pagefault_enable in kmap_atomic/kunmap_atomic

parisc: Call pagefault_disable/pagefault_enable in kmap_atomic/kunmap_atomic

Based on the generic implementation of kmap_atomic and kunmap_atomic,
we should call pagefault_disable and pagefault_enable in our PA8000
implementation.

The define for kmap_atomic_prot was also missing, and I updated
kmap_atomic_pfn to use the generic implementation because of the
change to kmap_atomic.

I believe that this change is needed to fix the fork copy-on-write
bug.

Signed-off-by: John David Anglin <[email protected]>
Signed-off-by: Kyle McMartin <[email protected]>