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

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.

Fix atmega328pb AC patch

Add support for atmega328pb