Enhance GSI IO interface with FV3LAM to handle subdomain restart files

[hu5970]

When FV3LAM model start to use FMS2 interface for model IO, we found the model initialization is very slow for large domain runs.

The solution to initialization slowness is to set io_layout(2) >1. This will speed up the initialization time a lot but it generates multiple subdomain restart files instead of one restart file for whole domain.

GSI needs function to read and write subdomain restart files when model has io_layout(2) > 1.