hw/intc/arm_gicv3: Replace mis-used MEMTX_* constants by booleans

hw/intc/arm_gicv3: Replace mis-used MEMTX_* constants by booleans

Quoting Peter Maydell:

  These MEMTX_* aren't from the memory transaction API functions;
  they're just being used by gicd_readl() and friends as a way to
  indicate a success/failure so that the actual MemoryRegionOps
  read/write fns like gicv3_dist_read() can log a guest error.
  Arguably this is a bit of a misuse of the MEMTX_* constants and
  perhaps we should have gicd_readl etc return a bool instead.

Follow his suggestion and replace the MEMTX_* constants by
boolean values, simplifying a bit the gicv3_dist_read() /
gicv3_dist_write() handlers.

Suggested-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20210826180704.2131949-3-philmd@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>