wifi: Add utility for struct conversions

Add a new utility file (hidl_struct_util) which would contain helper
functions to convert legacy HAL structures to HIDL structures and vice
versa.
Added utility functions to convert:
1. Background scan params from HIDL to legacy.
2. Scan Result from legacy to HIDL.
3. Cached Scan results from legacy to HIDL.
4. Link layer stats from legacy to HIDL.

Bug: 31991459
Test: Compiles
Change-Id: I48a49b43d425f8cc3059241c4bd652b2346f2381