x86/cpuid: Introduce struct cpuid_policy

x86/cpuid: Introduce struct cpuid_policy

struct cpuid_policy will eventually be a complete replacement for the cpuids[]
array, with a fixed layout and named fields to allow O(1) access to specific
information.

For now, the CPUID content is capped at the 0xd and 0x8000001c leaves, which
matches the maximum policy that the toolstack will generate for a domain.  The
xstate leaves extend up to LWP, and the structured features leaf is
implemented with subleaf properties (in anticipation of subleaf 1 appearing
soon), although only subleaf 0 is currently implemented.

Introduce calculate_raw_policy() which fills raw_policy with information,
making use of the new helpers, cpuid_{,count_}leaf().

Finally, rename calculate_featuresets() to init_guest_cpuid(), as it is going
to perform rather more work.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>