ASoC: amd: acp: declare and add prefix to 'bt_uart_enable' symbol

Sparse reports the following warning:

sound/soc/amd/acp-pcm-dma.c:39:6: error: symbol 'bt_uart_enable' was
not declared. Should it be static?

It's not very good practice to export such symbols that can easily
conflict, add the acp_ prefix and add declaration in header file.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20210907184216.33067-1-pierre-louis.bossart@linux.intel.com


Signed-off-by: Mark Brown <broonie@kernel.org>