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

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