x86/shadow: fold sh_x86_emulate_{write,cmpxchg}() into their only callers

x86/shadow: fold sh_x86_emulate_{write,cmpxchg}() into their only callers

The functions have a single caller only and are now guest paging type
independent (except for the tracing part), so have no need to exist as
standalone ones, let alone multiple times. Replace the two prior hooks
with just a single one for dealing with tracing.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Tim Deegan <tim@xen.org>