mkproject.sh: Do not override TEMPLATECONF if already set.

This will allow to pass a TEMPLATECONF path with a predefined
local.conf.template and bblayers.conf.template that will allow
to customize those files.

https://jira.digi.com/browse/DEL-468

Signed-off-by: Alex Gonzalez <alex.gonzalez@digi.com>

sdk/mkproject.sh

@@ -62,7 +62,7 @@ check_selected_platform() {
 }
 
 do_mkproject() {
-	export TEMPLATECONF="${MKP_CONFIGPATH}/${MKP_PLATFORM}"
+	export TEMPLATECONF="${TEMPLATECONF:-${MKP_CONFIGPATH}/${MKP_PLATFORM}}"
 	source ${MKP_SCRIPTPATH}/sources/poky/oe-init-build-env .
 	unset TEMPLATECONF