meta-phosphor: phosphor-debug-collector: Add symlink as git

Add a symbolic link to phosphor-debug-collector.bb named _git.bb and sets the
preferred version for the recipe.

Change-Id: Ie610746991dbb0bb20d8eb1efcebec3b185ec01c
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/conf/distro/include/phosphor-defaults.inc b/conf/distro/include/phosphor-defaults.inc
index 72fab7b..764a62d 100644
--- a/conf/distro/include/phosphor-defaults.inc
+++ b/conf/distro/include/phosphor-defaults.inc
@@ -252,3 +252,4 @@
 PREFERRED_VERSION_phosphor-ipmi-host = "1.0"
 PREFERRED_VERSION_phosphor-dbus-monitor = "1.0"
 PREFERRED_VERSION_mboxd = "1.0"
+PREFERRED_VERSION_phosphor-debug-collector = "1.0"