i386: Add new -IBRS versions of Intel CPU models

i386: Add new -IBRS versions of Intel CPU models

The new MSR IA32_SPEC_CTRL MSR was introduced by a recent Intel
microcode updated and can be used by OSes to mitigate
CVE-2017-5715.  Unfortunately we can't change the existing CPU
models without breaking existing setups, so users need to
explicitly update their VM configuration to use the new *-IBRS
CPU model if they want to expose IBRS to guests.

The new CPU models are simple copies of the existing CPU models,
with just CPUID_7_0_EDX_SPEC_CTRL added and model_id updated.

Cc: Jiri Denemark <[email protected]>
Signed-off-by: Eduardo Habkost <[email protected]>
Message-Id: <20180109154519[email protected]>
Signed-off-by: Eduardo Habkost <[email protected]>