hw/intc: clean-up error reporting for failed ITS cmd

hw/intc: clean-up error reporting for failed ITS cmd

While trying to debug a GIC ITS failure I saw some guest errors that
had poor formatting as well as leaving me confused as to what failed.
As most of the checks aren't possible without a valid dte split that
check apart and then check the other conditions in steps. This avoids
us relying on undefined data.

I still get a failure with the current kvm-unit-tests but at least I
know (partially) why now:

  Exception return from AArch64 EL1 to AArch64 EL1 PC 0x40080588
  PASS: gicv3: its-trigger: inv/invall: dev2/eventid=20 now triggers an LPI
  ITS: MAPD devid=2 size = 0x8 itt=0x40430000 valid=0
  INT dev_id=2 event_id=20
  process_its_cmd: invalid command attributes: invalid dte: 0 for 2 (MEM_TX: 0)
  PASS: gicv3: its-trigger: mapd valid=false: no LPI after device unmap
  SUMMARY: 6 tests, 1 unexpected failures

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20211112170454.3158925-1-alex.bennee@linaro.org
Cc: Shashi Mallela <shashi.mallela@linaro.org>
Cc: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>