downloads.mk: introduce name-agnostic PROJECT_GIT variable

Introduce a name-agnostic PROJECT_GIT variable poiting to
https://git.openwrt.org/ and declare LEDE_GIT and OPENWRT_GIT
as aliases to it.

After some transition time we can drop this alias variables.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

include/download.mk

@@ -6,8 +6,10 @@
 # See /LICENSE for more information.
 #
 
-OPENWRT_GIT = http://git.openwrt.org
-LEDE_GIT = https://git.lede-project.org
+PROJECT_GIT = https://git.openwrt.org
+
+OPENWRT_GIT = $(PROJECT_GIT)
+LEDE_GIT = $(PROJECT_GIT)
 
 ifdef PKG_SOURCE_VERSION
 PKG_VERSION ?= $(if $(PKG_SOURCE_DATE),$(PKG_SOURCE_DATE)-)$(call version_abbrev,$(PKG_SOURCE_VERSION))