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

common: Fix a few patches

- Fix some descriptions
- Rename ambiguous WDT options

atmega1280: Factor out USART into a common patch

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