x86/svm: Improvements using named features

x86/svm: Improvements using named features

This avoids calling into hvm_cpuid() to obtain information which is directly
available.  In particular, this avoids the need to overload flag_dr_dirty
because of hvm_cpuid() being unavailable in svm_save_dr().

flag_dr_dirty is returned to a boolean (as it was before c/s c097f549 which
introduced the need to overload it).  While returning it to type bool, remove
the use of bool_t for the adjacent fields.

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