Fix order-dependent tests; Enforce SoC when opt-in FP16

[qti-yuduo]

Motivation

Test case now is order-dependent, it would fail if order isn't preserved. This is because SDK has cache and not stateless.

Changes:

• Enforce SoC (can't be unknown) when enable_htp_fp16_precision is set; This allow fail fast. Less confusing. (this is consistent with BF16 support).
• Add missing Windows V68 skip guard. Make it explicit. Hidden in macro is confusing.
• TearDown soc_model reset no longer useful -- removed.
• SetUp, remove early return so we can actually query on Linux.
• Test name consistency, _FP32_as_FP16 for all relevant tests.