docs: dt: writing-bindings: Express better expectations of "specific"

Devicetree bindings are supposed to be specific in terms of compatibles
and other properties.  Short "specific" has many implications, so extend
the description to cover them:

1. Mention no family names and avoid generic SoC fallbacks in
   compatible.  The list grew, mixing DO's and DON'T's, so split it into
   multiple items.

2. No properties implied by the compatible.

3. Document desired lack of ABI impact and acceptable solution if such
   needs arises: clearly marking it in commit msg.

All above follows established Devicetree bindings maintainers review
practice, so no new rules in practice are introduced here.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20250707095019.66792-5-krzysztof.kozlowski@linaro.org


Signed-off-by: Rob Herring (Arm) <robh@kernel.org>