enable binascii in microbit_v2 build

[jerryneedell]

ampy and rshell both import ubinascii when reading files from a device.
I modified ampy to import binascii if ubinascii is not avaliable

py$ diff files.py files.py.save 
62,65c62
<             try:
<                 import ubinascii
<             except:
<                 import binascii as ubinascii
---
>             import ubinascii
110c107
<                 try:
---
>                 try:        

This PR enables binascii in the microbit_v2 build so it is possible to use ampy ( and possible rshell with a similar fix)
I have tested this with a microbit_v2 and my modified ampy and it is working

prior to this PR, a "get" failed with

jerryneedell@jerryneedell-ubuntu-macmini:~/projects/microbit_v2$ ampy  get code.py
Traceback (most recent call last):
  File "/home/jerryneedell/.local/bin/ampy", line 8, in <module>
    sys.exit(cli())
  File "/home/jerryneedell/.local/lib/python3.8/site-packages/click/core.py", line 829, in __call__
    return self.main(*args, **kwargs)
  File "/home/jerryneedell/.local/lib/python3.8/site-packages/click/core.py", line 782, in main
    rv = self.invoke(ctx)
  File "/home/jerryneedell/.local/lib/python3.8/site-packages/click/core.py", line 1259, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/home/jerryneedell/.local/lib/python3.8/site-packages/click/core.py", line 1066, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/home/jerryneedell/.local/lib/python3.8/site-packages/click/core.py", line 610, in invoke
    return callback(*args, **kwargs)
  File "/home/jerryneedell/.local/lib/python3.8/site-packages/ampy/cli.py", line 126, in get
    contents = board_files.get(remote_file)
  File "/home/jerryneedell/.local/lib/python3.8/site-packages/ampy/files.py", line 85, in get
    raise ex
  File "/home/jerryneedell/.local/lib/python3.8/site-packages/ampy/files.py", line 77, in get
    out = self._pyboard.exec_(textwrap.dedent(command))
  File "/home/jerryneedell/.local/lib/python3.8/site-packages/ampy/pyboard.py", line 279, in exec_
    raise PyboardError('exception', ret, ret_err)
ampy.pyboard.PyboardError: ('exception', b'', b'Traceback (most recent call last):\r\n  File "<stdin>", line 6, in <module>\r\nImportError: no module named \'binascii\'\r\n')

with binascii enabled

jerryneedell@jerryneedell-ubuntu-macmini:~/projects/microbit_v2$ ampy  get code.py
print("Hello World!")

I plan to submit a PR to ampy to to implement the changes I had to make to use it.

[dhalbert]

Thanks! One style change, and we'll need to see if it fits.

[dhalbert]

👍