esp32/modules: Use "from machine import *" instead of __getattr__.

The esp32 port has the machine Counter and Encoder classes implemented in
Python, requiring a `machine.py` that extends the built-in machine module.

That previously used `__getattr__()` to delegate lookups to the built-in,
but that means any failed lookup raises an `AttributeError` instead of an
`ImportError`.  This means (among other things) that certain tests like
CAN and I2CTarget would fail because they couldn't skip the test correctly.

This commit improves the situation by using `from machine import *` instead
of `__getattr__()`, which puts all the built-in functions/classes/constants
directly in the `machine.py` global namespace.  That means an `ImportError`
is now correctly raised for attributes that don't exist.

Although this takes up a bit more RAM, it's now a lot faster to import from
the machine module: what used to take around 100us to lookup a name now
takes only 5us.

Signed-off-by: Damien George <damien@micropython.org>

Author: dpgeorge

ports/esp32/modules/machine.py

@@ -3,7 +3,7 @@
 _path = sys.path
 sys.path = ()
 try:
-    import machine as _machine
+    from machine import *
 finally:
     sys.path = _path
     del _path
@@ -185,8 +185,3 @@ def phases(self):
 
 
 del esp32
-
-
-# Delegate to built-in machine module.
-def __getattr__(attr):
-    return getattr(_machine, attr)