vVMX: use latched VMCS machine address

vVMX: use latched VMCS machine address

Instead of calling domain_page_map_to_mfn() over and over, latch the
guest VMCS machine address unconditionally (i.e. independent of whether
VMCS shadowing is supported by the hardware).

Since this requires altering the parameters of __[gs]et_vmcs{,_real}()
(and hence all their callers) anyway, take the opportunity to also drop
the bogus double underscores from their names (and from
__[gs]et_vmcs_virtual() as well).

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Tested-by: Liang Z Li <liang.z.li@intel.com>
Acked-by: Kevin Tian <kevin.tian@intel.com>