libs/guest: introduce xc_cpu_policy_t

libs/guest: introduce xc_cpu_policy_t

Introduce an opaque type that is used to store the CPUID and MSRs
policies of a domain. Such type uses the existing {cpuid,msr}_policy
structures to store the data, but doesn't expose the type to the users
of the xenguest library. There are also two arrays to allow for easier
serialization without requiring an allocation each time.

Introduce an allocation (init) and freeing function (destroy) to
manage the type.

Note the type is not yet used anywhere.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>