conf: add /var/lib/alsa/card<NUMBER>.conf.d directory lookups

It may be handy to put extra configurations or symlinks to
the global runtime directory. The configurations may be
created at boot / hotplug event by udev or other scripts.

Signed-off-by: Jaroslav Kysela <perex@perex.cz>

src/conf/alsa.conf

@@ -57,6 +57,14 @@ cards.@hooks [
 					".conf"
 				]
 			}
+			{
+				@func concat
+				strings [
+					"/var/lib/alsa/card"
+					{ @func private_integer }
+					".conf.d"
+				]
+			}
 		]
 		errors false
 	}