x86/HVM: fix x2APIC APIC_ID read emulation

x86/HVM: fix x2APIC APIC_ID read emulation

APIC and x2APIC have different format for APIC_ID register. Need
translation.

Signed-off-by: Zhenguo Wang <wangzhenguo@huawei.com>
Signed-off-by: Xiaowei Yang <xiaowei.yang@huawei.com>
Convert code to use switch(), fixing coding style issue at once, and
use GET_xAPIC_ID() on the value read instead of VLAPIC_ID() (reading
the field again).

In the course of this also properly reject both read and writes on the
non-existing MSR corresponding to APIC_ICR2.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Keir Fraser <keir@xen.org>