efpga: Adjust address width

Created by: zarubaf

@gmartin102 I got an error when using Verilator because ADDR_WIDTH wasn't defined there. I took the next closest match APB_FPGA_ADDR_WIDTH and since I am not sure whether this is correct I am proposing this fix here and looking for your correction :-D

Signed-off-by: florian@openhwgroup.org