Added tools/lib-multiboot API to support flash access through Etherbone.

- eb/etherbone.py: python API wapper using Etherbone libaray
- eb/eb.py: xil_multiboot device class with direct register access
- flash_m25p.py: M25P flash IO class
- xil_multiboot.py: top class that supports all ICAP/flash on target
- mbtest.py: __main__ test script that proofs a successful flash reading & erasing