x86/cpuid: Drop the temporary linear feature bitmap from struct cpuid_policy

x86/cpuid: Drop the temporary linear feature bitmap from struct cpuid_policy

With most uses of the *_featureset API removed, the remaining uses are only
during XEN_SYSCTL_get_cpu_featureset, init_guest_cpuid(), and
recalculate_cpuid_policy(), none of which are hot paths.

Drop the temporary infrastructure, and have the current users recreate the
linear bitmap using cpuid_policy_to_featureset().  This avoids storing
duplicated information in struct cpuid_policy.

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