hw/intc/arm_gicv3_its: Factor out "find ITE given devid, eventid"

hw/intc/arm_gicv3_its: Factor out "find ITE given devid, eventid"

The operation of finding an interrupt table entry given a (DeviceID,
EventID) pair is necessary in multiple different ITS commands.  The
process requires first using the DeviceID as an index into the device
table to find the DTE, and then useng the EventID as an index into
the interrupt table specified by that DTE to find the ITE.  We also
need to handle all the possible error cases: indexes out of range,
table memory not readable, table entries not valid.

Factor this out into a separate lookup_ite() function which we
can then call from the places where we were previously open-coding
this sequence. We'll also need this for some of the new GICv4.0
commands.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20220408141550.1271295-12-peter.maydell@linaro.org