x86/vlapic: fixes for HVM code when running without a vlapic

x86/vlapic: fixes for HVM code when running without a vlapic

The HVM related code (SVM, VMX) generally assumed that a local apic is
always present. With the introduction of a HVM mode were the local apic can
be removed, some of this broken code paths arised.

The SVM exit/resume paths unconditionally checked the state of the lapic,
which is wrong if it's been disabled by hardware, fix this by adding the
necessary checks. On the VMX side, make sure we don't add mappings for a
local apic if it's disabled.

In the generic vlapic code, add checks to prevent setting the TSC deadline
timer if the lapic is disabled, and also prevent trying to inject interrupts
from the PIC is the lapic is also disabled.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Kevin Tian <kevin.tian@intel.com>