[ROCm] add MAGMA_HOME env var hint to cmake, centos-rocm Dockerfile (#54511)
Summary:
MAGMA_HOME was previously set for the ubuntu-rocm/Dockerfile. However, this missed centos builds as well as any builds that do not use the CI image environments.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/54511
Reviewed By: jbschlosser
Differential Revision: D27755983
Pulled By: malfet
fbshipit-source-id: 1ffd2cd100f4221c2bb64e6915fa3372ee1f6247
