Linux: bypass: consolidate copy_page macros into a single function

Linux: bypass: consolidate copy_page macros into a single function

The copy_page(s) macros are very similar; combine them into a
single function that can be used for all cases.

This will make it easier to add some pre-processor logic around
the kmap_atomic calls to adapt to Linux API changes.

Reviewed-on: http://gerrit.openafs.org/7980
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>
(cherry picked from commit 0a8256a26fafb490b454f2a857b0c15d859572c5)

Change-Id: I6835a024428b26a8cd8d073f6304d0d0b3042b24
Reviewed-on: http://gerrit.openafs.org/8077
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Reviewed-by: Ken Dreyer <ktdreyer@ktdreyer.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>