add SandyBridge CPU model

This patches add the definition of a SandyBridge CPU model.

Summary of differences:

Flags present on actual hardware, but not on the added model definition:

- pbe, tm, ht, ss, acpi, vme, xTPR, tm2, eist, smx: host-specific
  features, not exposed to guest.
- ds, ds-cpl, dtes64, pdcm: emulation not supported by KVM (although it
  may be added in the future if implementing PMU virtualization)
- pcid, vmx, monitor: not emulated by Qemu/KVM right now.
- osxsave: set by the guest OS, not by Qemu.

Flags added, that were not present on Westmere model:

- xsave: already supported by Qemu
- avx, pclmulqdq: all new state the new instructions could use is
  handled by xsave state loading/saving code.
- tsc-deadline, x2apic, rdtscp: already supported by Qemu/KVM.

Below there's a comparison of the features on the current Westmere CPU
model, and the SandyBridge CPU model.

- The "full" line contains the flags found on actual hardware.
- The "missing" line shows the flags that are present on actual
  hardware, but not on the added SandyBridge model.
- The "new" line shows the flags that were not on the Westmere model,
  but are on SandyBridge.

feature_edx:
  Westmere:                 sse2 sse fxsr mmx         clflush pse36 pat cmov mca pge mtrr sep apic cx8 mce pae msr tsc pse de     fpu
  full:        pbe tm ht ss sse2 sse fxsr mmx ds acpi clflush pse36 pat cmov mca pge mtrr sep apic cx8 mce pge msr tsc pse de vme fpu
  SandyBridge:              sse2 sse fxsr mmx         clflush pse36 pat cmov mca pge mtrr sep apic cx8 mce pae msr tsc pse de     fpu
  missing:     pbe tm ht ss                   ds acpi                                                                         vme

feature_ecx:
  Westmere:                      aes              popcnt        sse4.2 sse4.1                cx16 ssse3                                                  sse3
  full:        avx osxsave xsave aes tsc-deadline popcnt x2apic sse4.2 sse4.1 pcid pdcm xTPR cx16 ssse3 tm2 eist smx vmx ds-cpl monitor dtes64 pclmulqdq sse3
  SandyBridge: avx         xsave aes tsc-deadline popcnt x2apic sse4.2 sse4.1                cx16 ssse3                                        pclmulqdq sse3
  missing:         osxsave                                                    pcid pdcm xTPR            tm2 eist smx vmx ds-cpl monitor dtes64
  new:         avx         xsave     tsc-deadline        x2apic                                                                                pclmulqdq

extfeature_edx:
  Westmere:    i64        nx syscall
  full:        i64 rdtscp nx syscall
  SandyBridge: i64 rdtscp nx syscall
  new:             rdtscp

extfeature_ecx:
  Westmere:    lahf_lm
  full:        lahf_lm
  SandyBridge: lahf_lm

Cc: "Dugger, Donald D" <donald.d.dugger@intel.com>
Cc: "Zhang, Xiantao" <xiantao.zhang@intel.com>
Acked-by: Xiantao Zhang <xiantao.zhang@intel.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
