[NPU][IE-MDK] Add fallbacks for platform indentification

[sbutnari]

Details:

• The skip config gets multiple fallbacks for platform identification.
• Some tests can set their own desired platform, while the skip config is populated before any test is run. This means that it needs to know what's the expected platform, in order to populate the list correctly.
• This implementation uses IE_NPU_TESTS_PLATFORM as the first source form platform identification, as it's a mandatory envvar to run ov_npu_func_tests. It then falls back to using IE_NPU_TESTS_DEVICE_NAME. If neither envvar provide a usable platform, the final fallback is the list returned by the NPU Plugin

Tickets:

• E 189860