Hi Stafford,
I've tested the "brcm,bcm6345-gpio" driver with the OpenCores 8-bit GPIO core, and it is working as expected.
For reference, here is the hardware connection logic I used for the OpenRISC to OpenCores GPIO interface:
Verilog:
simple_gpio gpio0 (
    .clk_i  (clk_i),
    .rst_i  (rst_i),
    .cyc_i  (cyc_i & (|sel_i)),
    .stb_i  (stb_i & (|sel_i)),
    .adr_i  (adr_i[2]),
    .we_i   (we_i),
    .dat_i  (dat_i[7:0]),
    .ack_o  (ack_o),
    .dat_o  (dat_o[7:0]),
    .gpio   (gpio[7:0]),
    .gpio_i (gpio_i)
);
And here is the corresponding part of my dts:
gpio0: gpio@91000000 {
    compatible = "brcm,bcm6345-gpio";
    reg = <0x91000000 0x4>, <0x91000004 0x4>;
    reg-names = "dat", "dirout";
    gpio-controller;
    big-endian; 
    status = "okay";