hw/intc/arm_gicv3_its: Implement GITS_BASER2 for GICv4

hw/intc/arm_gicv3_its: Implement GITS_BASER2 for GICv4

The GICv4 defines a new in-guest-memory table for the ITS: this is
the vPE table.  Implement the new GITS_BASER2 register which the
guest uses to tell the ITS where the vPE table is located, including
the decode of the register fields into the TableDesc structure which
we do for the GITS_BASER<n> when the guest enables the ITS.

We guard provision of the new register with the its_feature_virtual()
function, which does a check of the GITS_TYPER.Virtual bit which
indicates presence of ITS support for virtual LPIs.  Since this bit
is currently always zero, GICv4-specific features will not be
accessible to the guest yet.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20220408141550.1271295-8-peter.maydell@linaro.org