[PARISC] Define pgprot_noncached macro in pgtable.h

drivers/infiniband depends on definition of pgprot_noncached() macro.
Someone else will have to fix it's wrong.

Signed-off-by: Grant Grundler <grundler@parisc-linux.org>

Signed-off-by: Kyle McMartin <kyle@parisc-linux.org>