Cache bypass: Remove AFS_KMAP_ATOMIC

Cache bypass: Remove AFS_KMAP_ATOMIC

Since AFS_KMAP_ATOMIC is defined unconditionally, remove the ifdefs
and the code for the !AFS_KMAP_ATOMIC case.  We probably don't want
to support this feature on a kernel old enough not to have kmap_atomic.
This should exist on all 2.6 and even 2.4 linux kernels.

This simplifies the code for maintenance and later changes.

Reviewed-on: http://gerrit.openafs.org/3372
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit 1de6d5bb0122d00c398202451bf88042ea08aa3e)

Change-Id: I6d2970f9b8811e145e2a03105c64cbd6714c0c5a
Reviewed-on: http://gerrit.openafs.org/3641
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>