hw/intc/arm_gicv3: Implement GICv3 distributor registers

Implement the distributor registers of a GICv3.

Signed-off-by: Shlomo Pongratz <shlomo.pongratz@huawei.com>
Reviewed-by: Shannon Zhao <shannon.zhao@linaro.org>
Tested-by: Shannon Zhao <shannon.zhao@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1465915112-29272-12-git-send-email-peter.maydell@linaro.org
[PMM: significantly overhauled/rewritten:
 * use the new bitmap data structures
 * restructure register read/write to handle different width accesses
   natively, since almost all registers are 32-bit only, rather
   than implementing everything as byte accesses
 * implemented security extension support
]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
