Separate discovery complete method from bta_dm_search_cmpl

Separate logic related to GATT service discovery finish from device
search complete handler.

Service discovery callback need to be called just in one case - when
GATT discovery is finished. In remaining cases, search complete is
enough.

Bug: 335732980
Bug: 330675788
Flag: com.android.bluetooth.flags.separate_service_and_device_discovery
Test: mma -j32
Change-Id: Icf238a7c70d1dc685adf87a6a90f7a872054a9c2