KVM: SVM: Add irqchip_split() checks before enabling AVIC

SVM AVIC hardware accelerates guest write to APIC_EOI register
(for edge-trigger interrupt), which means it does not trap to KVM.

So, only enable SVM AVIC only in split irqchip mode.
(e.g. launching qemu w/ option '-machine kernel_irqchip=split').

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Fixes: 44a95dae

 ("KVM: x86: Detect and Initialize AVIC support")
[Removed pr_debug - Radim.]
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>