fix: atmegaX8 TIFR should be read-write

fix: attiny84 ADCSRA should be read-write

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

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

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

Make the PINx registers writeable

Fix typo in ATtiny85 docs

Add basic support for ATmega168

attiny88: simplify patches thanks to svdpatch fixes

svdpatch: Fix _replace_enum when used on derived fields

Make sure the enum is replaced properly in the case of derived
enumerated values.

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

svdpatch: Fix peripheral modifications