Cleanup tBTA_DM_SERVICE_DISCOVERY_CB

Organize variables:
- first things that stay through whole stack life
- then things specific to device being searched
- then things for SDP
- then things for GATT

Bug: 330675788
Bug: 335732980
Flag: com.android.bluetooth.flags.separate_service_and_device_discovery
Test: mma -j32
Change-Id: I635dd29dacaa3668098da2b640ad1b55b415dc3a