Refactor path arguments to tosa-tools

tosa_verif_conformance_generator
- Move to using ref-model-path instead of ref-model-dir
- Add schema-path and flatc-path
- Add model_files module to locate default places for files
convert2conformance
- Remove default paths
verifier
- Switch to using exact path of verifier library
tosa_verif_run_tests
- Use conformance model_files to locate defaults

Change-Id: Ieca3b164670e2a7dcb047743667cc4e8317daa97
Signed-off-by: Josef Malmström <josef.malmstrom@arm.com>
Signed-off-by: Jeremy Johnson <jeremy.johnson@arm.com>