Add ATmega8U2

atmega328p, pb: Split EIMSK INT field into 2

The INT0 and INT1 fields in the EIMSK register were incorrectly
combined into a 2 bit field, split into individual bits.

Also allow write access to PRR0 and PRR1 in ATmega328PB.

atmega328p: Make PRR register writable

Fix 16bit timer patch

Add attiny841 and attiny861

Fix atmega328pb AC patch

Add basic support for ATmega4809

atmega64: Patch UMSELn fields in USART

These fields for some reason have a wrong bit range in the ATDF file.

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

patch: spi: Patch enumerated values for SPI prescaler

Rename the values for the SPI clock prescaler from VAL_0xXX to more
meaningful identifiers.

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

Add support for atmega328pb

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