cpu: Add SandyBridge-IBRS CPU model
cpu: Add SandyBridge-IBRS CPU model

This is a variant of SandyBridge with indirect branch prediction
protection. The only difference between SandyBridge and SandyBridge-IBRS
is the added "spec-ctrl" feature.

The SandyBridge-IBRS model in QEMU is a bit different since SandyBridge
got several additional features since we added it in cpu_map.xml:
    arat, vme, xsaveopt

Adding them only to the -IBRS variant would confuse our CPU detection
code.

Signed-off-by: Jiri Denemark <62bdf77dc47919a4d59a91822129d14633cfca81@redhat.com>
Reviewed-by: Pavel Hrdina <d4772d05997b8abf035041e3b4f4996380ea7e7a@redhat.com>

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