Hexagon (target/hexagon/imported) arch import

Imported from the Hexagon architecture library
    imported/macros.def
        The macro definitions specify instruction attributes that are applied
        to each instruction that references the macro. The generator will
        recursively apply attributes to each instruction that used the macro.
    imported/allidefs.def
        Top level instruction definition file
    imported/*.idef
        Instruction definition files
        These files are input to the first phase of the generator
        (gen_semantics.c) to create a python include file with the
        instruction semantics and attributes.  The python include
        file is fed to the second phase to generate various header files.
    imported/encode*.def
        Instruction encoding bit patterns for every instruction

Signed-off-by: Taylor Simpson <tsimpson@quicinc.com>
Acked-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <1612763186-18161-19-git-send-email-tsimpson@quicinc.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>