VMX: fix interaction of APIC-V and Viridian emulation

VMX: fix interaction of APIC-V and Viridian emulation

Viridian using a synthetic MSR for issuing EOI notifications bypasses
the normal in-processor handling, which would clear
GUEST_INTR_STATUS.SVI. Hence we need to do this in software in order
for future interrupts to get delivered.

Based on analysis by Yang Z Zhang <yang.z.zhang@intel.com>.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Yang Zhang <yang.z.zhang@intel.com>