Restructure the bitmap_*_region() operations, to avoid code duplication.

Also reduces binary text size by about 100 bytes (ia64 arch).  The original
Bottomley bitmap_*_region patch added about 1000 bytes of compiled kernel text
(ia64).  The Mundt multiword extension added another 600 bytes, and this
restructuring patch gets back about 100 bytes.

But the real motivation was the reduced amount of duplicated code.

Tested by Paul Mundt using <= BITS_PER_LONG as well as power of
2 aligned multiword spanning allocations.
Signed-off-by: Paul Mundt <lethal@linux-sh.org>
Signed-off-by: Paul Jackson <pj@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>