KVM: selftests: Play nice with AMD's AVIC errata

KVM: selftests: Play nice with AMD's AVIC errata

When AVIC, and thus IPI virtualization on AMD, is enabled, the CPU will
virtualize ICR writes.  Unfortunately, the CPU doesn't do a very good job,
as it fails to clear the BUSY bit and also allows writing ICR2[23:0],
despite them being "RESERVED MBZ".  Account for the quirky behavior in
the xapic_state test to avoid failures in a configuration that likely has
no hope of ever being enabled in production.

Link: https://lore.kernel.org/r/20240719235107.3023592-11-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>