hw/intc/arm_gicv3_its: Split out process_its_cmd() physical interrupt code

hw/intc/arm_gicv3_its: Split out process_its_cmd() physical interrupt code

Split the part of process_its_cmd() which is specific to physical
interrupts into its own function.  This is the part which starts by
taking the ICID and looking it up in the collection table.  The
handling of virtual interrupts is significantly different (involving
a lookup in the vPE table) so structuring the code with one
sub-function for the physical interrupt case and one for the virtual
interrupt case will be clearer than putting both cases in one large
function.

The code for handling the "remove mapping from ITE" for the DISCARD
command remains in process_its_cmd() because it is common to both
virtual and physical interrupts.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20220408141550.1271295-14-peter.maydell@linaro.org