core: Add parameters to the synth job

[stffrdhrn]

THis allows us to run the synthesis with different configurations. For
example:

    fusesoc run --target synth mor1kx \
      --FEATURE_DATACACHE ENABLED \
      --FEATURE_DMMU ENABLED \
      --OPTION_DCACHE_BLOCK_WIDTH 4 \
      --OPTION_DCACHE_LIMIT_WIDTH 31 \
      --OPTION_DCACHE_SET_WIDTH 8 \
      --OPTION_DCACHE_WAYS 1 \
      --FEATURE_INSTRUCTIONCACHE ENABLED \
      --FEATURE_IMMU ENABLED \
      --OPTION_ICACHE_BLOCK_WIDTH 4 \
      --OPTION_ICACHE_LIMIT_WIDTH 31 \
      --OPTION_ICACHE_SET_WIDTH 8 \
      --OPTION_ICACHE_WAYS 1 \
      --OPTION_RF_NUM_SHADOW_GPR 1 \
      --FEATURE_ROR ENABLED \
      --FEATURE_EXT ENABLED \
      --FEATURE_FPU ENABLED > yosys.log ; grep -A10 'Number of cells' yosys.log

    INFO: Preparing ::mor1kx:5.0-r3
    INFO: Setting up project
    INFO: Setting up project
    INFO: Building
    INFO: Running
       Number of cells:              32484
	 SB_CARRY                      849
	 SB_DFF                        446
	 SB_DFFE                      9848
	 SB_DFFESR                     676
	 SB_DFFESS                      16
	 SB_DFFSR                       76
	 SB_DFFSS                        3
	 SB_LUT4                     20537
	 SB_RAM40_4K                    33

[stffrdhrn]

Requesting @olofk to have a look at this one as I am updating for mor1kx fusesoc core file.

[olofk]

That looks perfectly fine to me. Please go ahead

[stffrdhrn]

Thanks