XDR: decouple from system XDR implementation

XDR: decouple from system XDR implementation

Since commit 7293ddf325b149cae60d3abe7199d08f196bd2b9 we have stopped
trying to use the system-provided XDR implementation, but the xdr_ops
structure was still structured to accomodate for the old limitations
of the system XDR. Change xdr_ops so it is just always one consistent
structure.

This removes:

 - The AFS_XDR_64BITOPS define and all related code, since we never
   call the 64-bit versions of getint and putint ourselves

 - The rearrangement of getint32/putint32 depending if we are in
   Solaris kernel-land or not

 - The .x_control field

Change-Id: I59b7579da1ea728eaba6b426011adbe4f7a331b6
Reviewed-on: http://gerrit.openafs.org/2503
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>