x86: Drop struct old_cpu_policy

x86: Drop struct old_cpu_policy

With all the complicated callers of x86_cpu_policies_are_compatible() updated
to use a single cpu_policy object, we can drop the final user of struct
old_cpu_policy.

Update x86_cpu_policies_are_compatible() to take (new) cpu_policy pointers,
reducing the amount of internal pointer chasing, and update all callers to
pass their cpu_policy objects directly.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
(cherry picked from commit 66c5c99656314451ff9520f91cff5bb39fee9fed)