[NVPTX] Add builtin support for 'globaltimer' (#79765)

Summary:
This patch adds support for `globaltimer` to match `clock` and
`clock64`. See the PTX ISA reference for details. This patch does not
implement the `hi` or `lo` variants for brevity as they can be obtained
from this with the cost of an additional register.

https://docs.nvidia.com/cuda/parallel-thread-execution/index.html#special-registers-globaltimer-globaltimer-lo-globaltimer-hi