On CPython, and with pylint, the variables MATCH_ROM and SEARCH_ROM are
undefined.  This code works in MicroPython because these variables are
constants and the MicroPython parser/compiler optimises them out.  But it
is not valid Python because they are technically undefined within the scope
they are used.

This commit makes the code valid Python code.  The const part is removed
completely because these constants are part of the public API and so cannot
be moved to the global scope (where they could still use the MicroPython
const optimisation).

This is run with uncrustify 0.70.1, and black 19.10b0.

DS1822P sensors behave just like the DS18B20 except for the following:
- it has a different family code: 0x22
- it has only the GND and DQ pins connected, it uses parasitic power from
  the data line

Contributed by @nebelgrau77.

A previous version of the 1-wire driver (which was recently replaced by the
current one) had this behaviour and it allows to create a 1-wire bus
without any external pull-up resistors.

These drivers can now be used by any port (so long as that port has the
_onewire driver from extmod/modonewire.c).

These drivers replace the existing 1-wire and DS18X20 drivers in the
drivers/onewire directory.  The existing ones were pyboard-specific and
not very efficient nor minimal (although the 1-wire driver was written in
pure Python it only worked at large enough CPU frequency).

This commit brings backwards incompatible API changes to the existing
1-wire drivers.  User code should be converted to use the new drivers, or
check out the old version of the code and keep a local copy (it should
continue to work unchanged).

The driver seems to be be enabling the pullup resistor in most places, but
not this one. Making this one little change allows onewire devices to be
used with no external pullup resistor.