[ROCm] set ROCM_ARCH to gfx900 and gfx906 for CI builds (#47683)
Summary:
This change adds the arch settings for caffe2 builds, fixes some typos,
and clarifies that this setting applies to both CircleCI and Jenkins.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/47683
Reviewed By: zou3519
Differential Revision: D24864034
Pulled By: malfet
fbshipit-source-id: 304b8a8e5c929ddaeb9c399f6219783a1369d842
