Use the common page allocation helper for the xAPIC IPI test, effectively
raising the minimum virtual address from 0x1000 to 0x2000.  Presumably
the test won't explode if it can't get a page at address 0x1000...

Cc: Peter Shier <pshier@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210622200529.3650424-10-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>