QEMU: MCE: Add MCE simulation to qemu/tcg

- MCE features are initialized when VCPU is intialized according to CPUID.
- A monitor command "mce" is added to inject a MCE.
- A new interrupt mask: CPU_INTERRUPT_MCE is added to inject the MCE.

aliguori: fix build for linux-user

Signed-off-by: Huang Ying <ying.huang@intel.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
