all: Drop unnecessary access mode patches

Due to a change in atdf2svd [1], all these access mode patches are no
longer required - they are now translated correctly from the vendor
source file.

Drop all patches which no longer change the output (the code before and
after this change is equivalent when using the new atdf2svd).

[1]: https://github.com/Rahix/atdf2svd/commit/a189276b3540b647fab832946edf0acf39730a0e

fix: attiny84 ADCSRA should be read-write

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>

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