ALSA: hda/realtek: Enable 4-speaker output Dell Precision 5530 laptop

Just as with the 5570 (and the other Dell laptops), this enables the two
subwoofer speakers on the Dell Precision 5530 together with the main
ones, significantly increasing the audio quality. I've tested this
myself on a 5530 and can confirm it's working as expected.

Signed-off-by: Callum Osmotherly <callum.osmotherly@gmail.com>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/YyMjQO3mhyXlMbCf@piranha
Signed-off-by: Takashi Iwai <tiwai@suse.de>