Update cam for OpenACC rrtmgp data optimization

[gdicker1]

Bring in changes to EarthWorksOrg/CAM to address performance hits due to data transfers between CPU and GPU in RRTMGP.

[gdicker1]

This PR will move out of draft once the Sub-PR is merged and tagged (and the Externals.cfg is updated).

Sub-PR:

• https://github.com/EarthWorksOrg/CAM/pull/24