Makefile: Add OPL_VERSION based on git tags an format change

OPL_VERSION format slightly changed:

from (example):
  1.0.0.1598-Beta-2f39094-dirty-localversion

to (example):
  v1.0.0-Beta-1598-2f39094-dirty-localversion

Makefile

@@ -53,7 +53,14 @@ ifneq ($(shell test -d .git; echo $$?),0)
   DIRTY = -dirty
 endif
 
-OPL_VERSION = $(VERSION).$(SUBVERSION).$(PATCHLEVEL).$(REVISION)$(if $(EXTRAVERSION),-$(EXTRAVERSION))$(if $(GIT_HASH),-$(GIT_HASH))$(if $(DIRTY),$(DIRTY))$(if $(LOCALVERSION),-$(LOCALVERSION))
+GIT_TAG = $(shell git describe --exact-match --tags 2>/dev/null)
+ifeq ($(GIT_TAG),)
+	# git revision is not tagged
+	OPL_VERSION = v$(VERSION).$(SUBVERSION).$(PATCHLEVEL)$(if $(EXTRAVERSION),-$(EXTRAVERSION))-$(REVISION)$(if $(GIT_HASH),-$(GIT_HASH))$(if $(DIRTY),$(DIRTY))$(if $(LOCALVERSION),-$(LOCALVERSION))
+else
+	# git revision is tagged
+	OPL_VERSION = $(GIT_TAG)$(if $(DIRTY),$(DIRTY))
+endif
 
 FRONTEND_OBJS = pad.o fntsys.o renderman.o menusys.o OSDHistory.o system.o lang.o config.o hdd.o dialogs.o \
 		dia.o ioman.o texcache.o themes.o supportbase.o usbsupport.o ethsupport.o hddsupport.o \