Create ranges of reserved codec indexes for codec extensibility

The ranges BTAV_A2DP_CODEC_INDEX_SOURCE_EXT_MIN .. BTAV_A2DP_CODEC_INDEX_SOURCE_EXT_MAX
and BTAV_A2DP_CODEC_INDEX_SINK_EXT_MIN .. BTAV_A2DP_CODEC_INDEX_SINK_MIN
are reserved for offloaded codecs that are not recognized by the stack.

Bug: 308958546
Test: m Bluetooth
Change-Id: I52251fcf6fff2f7f14100b4ad7a60d741785a3b6