hw/intc: GICv3 ITS Command processing

Added ITS command queue handling for MAPTI,MAPI commands,handled ITS
translation which triggers an LPI via INT command as well as write
to GITS_TRANSLATER register,defined enum to differentiate between ITS
command interrupt trigger and GITS_TRANSLATER based interrupt trigger.
Each of these commands make use of other functionalities implemented to
get device table entry,collection table entry or interrupt translation
table entry required for their processing.

Signed-off-by: Shashi Mallela <[email protected]>
Reviewed-by: Peter Maydell <[email protected]>
Message-id: [email protected]
[PMM: use INTERRUPT for ItsCmdType enum name to avoid
 conflict with INT type defined by Windows headers]
Signed-off-by: Peter Maydell <[email protected]>

Author: shashi-j