cappuccino/rf: *really* fix RF_ADDR_WIDTH

As Stefan W pointed out to me, my previous fix
was completely incorrect and only correctly for
OPTION_RF_NUM_SHADOW_GPR = 1.
This is based on a patch he presented, but makes
use of the `clog2 macro to maintain compatibility with
icarus.

Also, remove the unused RF_WORDS localparam.

rtl/verilog/mor1kx_rf_cappuccino.v

@@ -74,8 +74,11 @@ module mor1kx_rf_cappuccino
     output [OPTION_OPERAND_WIDTH-1:0] execute_rfb_o
     );
 
-   localparam RF_ADDR_WIDTH = OPTION_RF_ADDR_WIDTH + OPTION_RF_NUM_SHADOW_GPR;
-   localparam RF_WORDS = OPTION_RF_WORDS * (OPTION_RF_NUM_SHADOW_GPR+1);
+`include "mor1kx_utils.vh"
+
+   localparam RF_ADDR_WIDTH = OPTION_RF_ADDR_WIDTH +
+                              ((OPTION_RF_NUM_SHADOW_GPR == 1) ? 1 :
+                               `clog2(OPTION_RF_NUM_SHADOW_GPR));
 
    wire [OPTION_OPERAND_WIDTH-1:0]    rfa_ram_o;
    wire [OPTION_OPERAND_WIDTH-1:0]    rfb_ram_o;