patch: Switch to upstream svdtools patch tool

Instead of using our locally vendored version of svdpatch, switch to the
upstream version maintained by the stm32-rs project:

    https://github.com/stm32-rs/svdtools

Signed-off-by: Rahix <rahix@rahix.de>

patches: Include _svd tag

The _svd: tag is needed for upstream svdtools to find the corresponding
svd file for each patch.

Signed-off-by: Rahix <rahix@rahix.de>

Add basic support for ATmega644

Prepare 0.2.2

Signed-off-by: Rahix <rahix@rahix.de>

Update CHANGELOG

Simplify ATtiny84 ADC patch

Extract common EXINT patch from tiny84/85

Extract common EEPROM patch from tiny84/85/88

Extract common USI patch from tiny84/85

Add PINx patch to ATtiny84

Update CHANGELOG

Add support for the ATtiny84

ATtiny85 TC0 patch also applies to ATtiny84

svdpatch: create fields element if register has no fields

Add atmega48p device support

Update CHANGELOG

Make the PINx registers writeable

Fix typo in ATtiny85 docs

Update CHANGELOG

make: Properly remove 'extern crate' lines

The previous sed expression would remove arbitrary lines which can break
easily.  Instead, only remove actual extern crate lines.

This will provide a seamless upgrade to the next svd2rust version which
contains commit 85615cb0bbc8 ("Use and generate code for Edition 2018
only ") and thus no longer emits 'extern crate' lines.

Signed-off-by: Rahix <rahix@rahix.de>