x86/HVM: extend LAPIC shortcuts around P2M lookups

x86/HVM: extend LAPIC shortcuts around P2M lookups

... to all internally handled MMIO regions. It is in particular the
HPET page that, e.g. on Windows Server 2012 R2, can get heavily
accessed, and hence avoiding the unnecessary lookups is rather
beneficial (in the reported case a 40+-vCPU guest would previously not
have booted at all while with hvm_hap_nested_page_fault() shortcut
alone it was able to boot up in 18 minutes [i.e. still room for
improvement]).

Note the apparently unrelated addition of a is_hvm_vcpu() check to the
__hvm_copy() code: Afaict for PVH this shortcut should never have taken
effect (since there's no LAPIC in that case).

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Tim Deegan <tim@xen.org>