HIP Memory Advise : Set managed memory to coarse grain

[WeiqunZhang]

For unsafe atomics to work on managed memory, we must set it to coarse
grain.

For gfx90a, we can explicitly use unsafeAtomicAdd.

Checklist

The proposed changes:

• fix a bug or incorrect behavior in AMReX
• add new capabilities to AMReX
• changes answers in the test suite to more than roundoff level
• are likely to significantly affect the results of downstream AMReX users
• include documentation in the code and/or rst files, if appropriate