meta-phosphor: Allow overriding of DISTRO_NAME

Some systems wish to override the distro name. Allow this by not
forcefully setting the variable in phosphor-base.

Change-Id: Ie6fc72e92d7bd215dfa6a2835a8022ae8daf51b2
Signed-off-by: Joel Stanley <joel@jms.id.au>
diff --git a/meta-phosphor/conf/distro/include/phosphor-base.inc b/meta-phosphor/conf/distro/include/phosphor-base.inc
index 3c90538..2af46f9 100644
--- a/meta-phosphor/conf/distro/include/phosphor-base.inc
+++ b/meta-phosphor/conf/distro/include/phosphor-base.inc
@@ -68,7 +68,7 @@
 require conf/distro/include/no-static-libs.inc
 require conf/distro/include/yocto-uninative.inc
 
-DISTRO_NAME = "Phosphor OpenBMC (Phosphor OpenBMC Project Reference Distro)"
+DISTRO_NAME ?= "Phosphor OpenBMC (Phosphor OpenBMC Project Reference Distro)"
 TARGET_VENDOR="-openbmc"
 
 VIRTUAL-RUNTIME_keymaps = ""