Fixes for arm example run for runner_util:prepare_input_tensors move (#1800)

Summary:
Fixes https://github.com/pytorch/executorch/issues/1569
When some of the files in extension/ were refactored and tidied up this broke the Arm example code which depended on one which had not yet been exported as a library from buck to the CMAKE builds. This fixes that up along with a few minor build issues that have ocurred on the examples/arm/run.sh execution.

Pull Request resolved: https://github.com/pytorch/executorch/pull/1800

Reviewed By: mergennachin

Differential Revision: D53488047

Pulled By: larryliu0820

fbshipit-source-id: 32a052d448e2602da84c6d0b30c244e87c25d234