Handle memory-mapped chips properly, needed for example on DECstations.
This support was in Linux 2.4 but for some reason got lost in 2.6.  This
patch is taken directly from the linux-mips repository.

[akpm@osdl.org: cleanup]
Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Signed-off-by: Martin Michlmayr <tbm@cyrius.com>
Cc: Paul Gortmaker <penguin@muskoka.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>