core: Add framework for an FPU

This adds the skeleton of a floating-point unit and implements the
mffs and mtfsf instructions.

Execute1 sends FP instructions to the FPU and receives busy,
exception, FP interrupt and illegal interrupt signals from it.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

Makefile

@@ -48,7 +48,7 @@ core_files = decode_types.vhdl common.vhdl wishbone_types.vhdl fetch1.vhdl \
 	cr_file.vhdl crhelpers.vhdl ppc_fx_insns.vhdl rotator.vhdl \
 	logical.vhdl countzero.vhdl multiply.vhdl divider.vhdl execute1.vhdl \
 	loadstore1.vhdl mmu.vhdl dcache.vhdl writeback.vhdl core_debug.vhdl \
-	core.vhdl
+	core.vhdl fpu.vhdl
 
 soc_files = $(core_files) wishbone_arbiter.vhdl wishbone_bram_wrapper.vhdl sync_fifo.vhdl \
 	wishbone_debug_master.vhdl xics.vhdl syscon.vhdl soc.vhdl \