[AMD] NFC: refactor atomic rmw lowering patterns (#6258)

- Use `select` operation instead of bitwise calculations;
- Split different approaches of atomicRMW lowering to different
functions;
- Introduce AtomicRMWEmmiter to manage these approaches;
- Skip runtime checks if contiguaity is proven on the compile time

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Signed-off-by: Ilya Veselov <iveselov.nn@gmail.com>

Author: joviliast