hw/intc/arm_gicv3_its: In MAPC with V=0, don't check rdbase field

hw/intc/arm_gicv3_its: In MAPC with V=0, don't check rdbase field

In the MAPC command, if V=0 this is a request to delete a collection
table entry and the rdbase field of the command packet will not be
used.  In particular, the specification says that the "UNPREDICTABLE
if rdbase is not valid" only applies for V=1.

We were doing a check-and-log-guest-error on rdbase regardless of
whether the V bit was set, and also (harmlessly but confusingly)
storing the contents of the rdbase field into the updated collection
table entry.  Update the code so that if V=0 we don't check or use
the rdbase field value.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20220201193207.2771604-12-peter.maydell@linaro.org