target/arm: Add a core count property

target/arm: Add a core count property

The cortex A53 TRM specifies that bits 24 and 25 of the L2CTLR register
specify the number of cores in the processor, not the total number of
cores in the system. To report this correctly on machines with multiple
CPU clusters (ARM's big.LITTLE or Xilinx's ZynqMP) we need to allow
the machine to overwrite this value. To do this let's add an optional
property.

Signed-off-by: Alistair Francis <alistair.francis@xilinx.com>
Message-id: ef01d95c0759e88f47f22d11b14c91512a658b4f.1520018138.git.alistair.francis@xilinx.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>