[CMake] Allow building for Blackwell+ GPUs

[BenWibking]

Summary

Updates the CMake configuation so it allows AMREX_CUDA_ARCH to be >= 10 without silently discarding this value. This is required to build AMReX for Blackwell or newer GPUs, which have sm_100 or higher.

Additional background

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

[BenWibking]

@ax3l If there is a simpler way to do this, let me know. The CUDA architecture helper seems to use a lot of old CMake-isms that might have more modern replacements.