x86/hvm: Move hvm_funcs.cpuid_intercept() handling into hvm_cpuid()

x86/hvm: Move hvm_funcs.cpuid_intercept() handling into hvm_cpuid()

This reduces the net complexity of CPUID handling by having all adjustments in
the same place.  Remove the now-unused hvm_funcs.cpuid_intercept
infrastructure.

The SYSCALL feature hiding is tweaked when moved.  In principle, an
administrator can choose to explicitly hide the SYSCALL feature from the
guest, as it has a separate feature bit.  If this is the case, the feature
shouldn't be set behind the back of the administrators wishes.  (Not that many
64bit OSes would function in this scenario.)  In reality, SYSCALL will always
be set in edx at this point.

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