Add HwModule::getRoutes method

This complements an existing setter, and is needed
for testing.

Bug: 205808571
Test: atest HalAudioV6_0GeneratorTest
Test: atest HalAudioV7_0GeneratorTest
Test: atest VtsHalAudioV6_0TargetTest
Test: atest VtsHalAudioV7_0TargetTest
Change-Id: Iabe9d02be93dfee329e2a12f125fbe4d8b934105
Merged-In: Iabe9d02be93dfee329e2a12f125fbe4d8b934105