KVM: selftests: Move APIC definitions into a separate file

Processor.h is a hodgepodge of definitions. Though the local APIC is
technically built into the CPU these days, move the APIC definitions
into a new header file: apic.h.

Signed-off-by: Jim Mattson <jmattson@google.com>
Reviewed-by: Oliver Upton <oupton@google.com>
Message-Id: <20210604172611.281819-9-jmattson@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>