modules/wishbone: Added basic Wishbone modules (initial commit)

Added:
- asynchronous SRAM bus -> Wishbone bridge (wb_async_bridge)
- Conmax interconnect (wb_conmax)
- GPIO port (wb_gpio_port)
- Very simple timer (wb_simple timer)
- Simple UART (wb_uart)
- Vectored Interrupt controller (wb_vic)
- Virtual UART (mmapped FIFO, wb_virtual_uart)
- wbgen2 core generator libraries (wbgen2)