coolrunner2: Fix invalid multiple fanouts of XOR/OR gates

coolrunner2: Fix invalid multiple fanouts of XOR/OR gates

In some cases where multiple output pins share identical combinatorial
logic, yosys would only generate one $sop cell and therefore one
MACROCELL_XOR cell to try to feed the multiple sinks. This is not valid,
so make the fixup pass duplicate cells when necessary. For example,
fixes the following code:

module top(input a, input b, input clk_, output reg o, output o2);

wire clk;

BUFG bufg0 (
    .I(clk_),
    .O(clk),
);

always @(posedge clk)
    o = a ^ b;
assign o2 = a ^ b;

endmodule