parisc: Avoid spurious inequivalent alias kernel error messages

This patch changes flush_dcache_page() to only print inequivalent alias error
messages on systems that require coherency.  Inequivalent aliases can occur on
systems that don't require coherency and this can cause spurious messages.

Signed-off-by: John David Anglin <dave.anglin@bell.net>
Signed-off-by: Helge Deller <deller@gmx.de>