meta-phosphor: set DISTRO_CODENAME

Back in 2018 we stopped including poky.conf by default and treated
phosphor as a separate distro.  One minor side-effect of this is that
the DISTRO_CODENAME is no longer defined, which is used in some misc.
locations such as os-release.  Mirror the current Poky codename with
the intention that we will keep this in sync as upstream moves along.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Iabbdd3f6046f2c7b8ffc81536ab4b47f8471ee20
diff --git a/meta-phosphor/conf/distro/include/phosphor-base.inc b/meta-phosphor/conf/distro/include/phosphor-base.inc
index 13e3065..642b19e 100644
--- a/meta-phosphor/conf/distro/include/phosphor-base.inc
+++ b/meta-phosphor/conf/distro/include/phosphor-base.inc
@@ -1,5 +1,8 @@
 require conf/distro/include/phosphor-defaults.inc
 
+# Match the distro codename from upstream poky.
+DISTRO_CODENAME ?= "langdale"
+
 # Override these in poky based distros
 POKY_DEFAULT_DISTRO_FEATURES = "largefile opengl ptest multiarch wayland vulkan"
 POKY_DEFAULT_EXTRA_RDEPENDS = "packagegroup-core-boot"