arch/microblaze: add new architecture

Add Microblaze architecture support.

This depends on EXPERIMENTAL, as upstream projects do not yet
include full support to build a modern microblaze compiler.
This is in the process of being updated, but is not currently
publicly accessible.

Signed-off-by: "David Holsgrove" <david.holsgrove@xilinx.com>
Message-Id: <9c93e18b3d68b19303f3.1348113870@localhost.localdomain>
PatchWork-ID: 185305

 # Compute sparc-specific values

 CT_DoArchTupleValues() {

     # That's the only thing to override

     if [ "${CT_ARCH_64}" = "y" ]; then

         CT_TARGET_ARCH="${CT_ARCH}64"

     fi

 }