time: widen wallclock seconds to 64 bits

time: widen wallclock seconds to 64 bits

Linux is in the process of converting their seconds representation to
64 bits, so in order to support it consistently we should follow suit
(which at some point in quite a few years we'd have to do anyway). To
represent this in struct shared_info we leverage a 32-bit hole in
x86-64's and arm's variant of the structure; for x86-32 guests the only
(reasonable) choice we have is to put the extension in struct
arch_shared_info.

A note on the conditional suppressing the xen_wc_sec_hi helper macro
definition in the ix86 case for hypervisor and tools: Neither of the
two actually need this, and its presence causes the tools to fail to
build (due to the inclusion of both the x86-64 and x86-32 variants of
the header).

As a secondary change, x86's do_platform_op() gets a pointless
initializer as well as a pointless assignment of that same variable
dropped.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Tim Deegan <tim@xen.org>
Acked-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>