romlib: Improve compilation flags definition

* Optimization flags were only provided for debug build.
* Set optimisation level to -O1
* Remove CFLAGS which is never used for romlib
* Remove the ignored -g flag from LDFLAGS

Change-Id: Id4b69026d8a322ed4cb0acf06c350f13d31571ad
Signed-off-by: Louis Mayencourt <louis.mayencourt@arm.com>

lib/romlib/Makefile

@@ -24,9 +24,9 @@ else
   Q :=
 endif
 
+LDFLAGS := --gc-sections -O1
 ifeq ($(DEBUG),1)
-   CFLAGS  := -g
-   LDFLAGS := -g --gc-sections -O1 -Map=$(MAPFILE)
+   LDFLAGS += -Map=$(MAPFILE)
 endif