[PARISC] parisc specific kmap API implementation for pa8800

This patch fixes the pa8800 at a gross level (there are still other
subtle incoherency issues which can still cause crashes and HPMCs).

What it does is try to force eject inequivalent aliases before they
become visible to the L2 cache (which is where we get the incoherence
problems).

A new function (parisc_requires_coherency) is introduced in
asm/processor.h to identify the pa8x00 processors (8800 and 8900)
which have the issue.

Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>
Signed-off-by: Kyle McMartin <kyle@parisc-linux.org>