Effects Factory changes for effects offload

audio_effects.conf - commented changes to illustrate the
addition of Proxy and sub effects to the conf file

Added an effectFactoryApi - EffectGetSubEffects for querying the
sub effect descriptors from the factory. This api is used by the Proxy
to get the sub effects

Added functions and data structures in factory code for
loading the sub effects

gSubEffectList - has the Proxies and their corresponding sub effects

- addSubEffect() - reads a sub effect node and adds to the gSubEffectList
- findSubEffect() - searches through the gSubEffectList to find a SubEffect

Bug: 8174034.

Change-Id: I25b0c62b2ad523a52337128b51469e628209ea3e
Signed-off-by: jpadmana <rpadmanaban.jayashree@gmail.com>