LINUX 5.6: define osi_timeval32_t for 32-bit Linux

LINUX 5.6: define osi_timeval32_t for 32-bit Linux

For 32-bit Linux (e.g., arch i586), AFS_LINUX_64BIT_KERNEL is not
defined, so osi_timeval32_t is defined as a typedef of the native
'timeval'.  However, as of commit
c766d1472c70d25ad475cf56042af1652e792b23 "y2038: hide
timeval/timespec/itimerval/itimerspec types" (Linux 5.6), the native
timeval struct is no longer available.  On such a kernel, the OpenAFS
build will fail because osi_timeval32_t is not properly defined.

Instead, add new conditionals to properly define osi_timeval32_t for
this platform.

Reviewed-on: https://gerrit.openafs.org/14216
Reviewed-by: Cheyenne Wills <cwills@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
(cherry picked from commit 9a5790cfbb8e7b1a4a2e832911c71da49f604c20)

Change-Id: I223d8407bf28e91ffb2669013c089053ae93feb3
Reviewed-on: https://gerrit.openafs.org/14234
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>