audio: Use hardcoded r_submix configuration with XML

There are several reasons why parsing the canonical XML
configuration for the remote submix module will not work
correctly (see the commend in the code).

Since de facto all vendors use the canonical configuration
XML for the remote submix, substitute parsing it with
a correct hardcoded version.

Bug: 205884982
Test: atest VtsHalAudioCoreTargetTest
Change-Id: Iddebf9baa73e8dc90ada1c9b1783c513abb59420