x86/hvm: Rework HVM_HCALL_invalidate handling

x86/hvm: Rework HVM_HCALL_invalidate handling

Sending an invalidation to the device model is an internal detail of
completing the hypercall; callers should not need to be responsible for it.
Drop HVM_HCALL_invalidate entirely and call send_invalidate_req() when
appropriate.

This makes the function boolean in nature, although the existing
HVM_HCALL_{completed,preempted} constants are kept to aid code clarity.  While
updating the return type, drop _do from the name, as it is redundant.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>