tools: switch existing users of xc_get_{system,domain}_cpu_policy

tools: switch existing users of xc_get_{system,domain}_cpu_policy

With the introduction of xc_cpu_policy_get_{system,domain} and
xc_cpu_policy_serialise the current users of
xc_get_{system,domain}_cpu_policy can be switched to the new
interface.

Note that xc_get_{system,domain}_cpu_policy is removed from the public
interface and the functions are made static, since there are still
internal consumers in xg_cpuid_x86.c

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