libaudiohal: Fix probing of the AIDL HAL presence

Since the AIDL HAL service is starting in parallel
with the audioserver, using `checkService` can result
in false negatives. Need to use `isDeclared` which
does the check based on the vendor manifest.

Bug: 205884982
Test: start cuttlefish with AIDL HAL enabled,
      look for `FactoryHal` tag in logcat
Change-Id: I17c4da17eb8172cdc2440070fe332b69b6d64c0e