fix: atmegaX8 TIFR should be read-write

patch: Restructure timer patches

Redesign timer patch file structure for better modularity.  Now,
`timer/<chip>.yaml` defines all timer peripherals for a chip and uses
peripheral-level includes for patching the actual peripheral.  The
actual peripheral patches live in `timer/dev/<type>.yaml`.

The intermediate `<chip>.yaml` file is needed because peripheral-level
includes are not allowed in top-level files.

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

common: Fix a few patches

- Fix some descriptions
- Rename ambiguous WDT options

atmega32u4, attiny85: Add tc0 patch

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