soundwire: sysfs: cleanup the logic for creating the dp0 sysfs attributes

There's no need to special-case the dp0 sysfs attributes, the
is_visible() callback in the attribute group can handle that for us, so
add that and add it to the attribute group list making the logic simpler
overall.

This is a step on the way to moving all of the sysfs attribute handling
into the default driver core attribute group logic so that the soundwire
core does not have to do any of it manually.

Cc: Vinod Koul <vkoul@kernel.org>
Cc: Bard Liao <yung-chuan.liao@linux.intel.com>
Cc: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Cc: Sanyog Kale <sanyog.r.kale@intel.com>
Cc: alsa-devel@alsa-project.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Tested-By: Vijendar Mukunda <Vijendar.Mukunda@amd.com>
Link: https://lore.kernel.org/r/2024013029-budget-mulled-5b34@gregkh


Signed-off-by: Vinod Koul <vkoul@kernel.org>