Don't sort selected devices when RLP does not exist

Currently we're sorting all devices by natural ordering when route
listing preferences are not set. However, we need to maintain the order
of selected devices in order to make sure the group leader persists as
the first device.

Bug: 388347018
Test: atest
Flag: com.android.media.flags.enable_output_switcher_device_grouping
Change-Id: I30c2c721e69559cba08d79a7c953e5c25d95673f