target/arm: Add Jazelle feature

This adds a feature bit indicating support of the (trivial) Jazelle
implementation if ARM_FEATURE_V6 is set or if the processor is arm926
or arm1026.  This fixes the issue that any BXJ instruction will
result in an illegal_op.  BXJ instructions will now check if the
architecture supports ARM_FEATURE_JAZELLE.

Signed-off-by: Portia Stephens <portia.stephens@xilinx.com>
Reviewed-by: Alistair Francis <alistair.francis@xilinx.com>
Message-id: 20170905211232.11092-1-portia.stephens@xilinx.com
[PMM: edited commit message and comment text a bit]
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>