x86/mm: Sharing overhaul style improvements

x86/mm: Sharing overhaul style improvements

The name 'shared_info' for the list of shared pages backed by a share frame
collided with the identifier also used for a domain's shared info page. To
avoid grep/cscope/etc aliasing, rename the shared memory token to 'sharing.

This patch only addresses style, and performs no functional changes. To ease
reviwing, the patch was left as a stand-alone last-slot addition to the queue
to avoid propagating changes throughout the whole series.

Signed-off-by: Andres Lagar-Cavilla <andres@lagarcavilla.org>
Acked-by: Tim Deegan <tim@xen.org>
Committed-by: Tim Deegan <tim@xen.org>