drivers: memory: Add missing FORCE for generation of emif-asm-offsets

According to Documentation/kbuild/makefiles.txt all build targets using
if_changed should use FORCE as well. Add missing FORCE to make sure
emif-asm-offsets targets are rebuilt properly. Additionally, add
emif-asm-offsets.s to the $(target) list as described in the same
document to avoid it being built when unnecessary.

Signed-off-by: Dave Gerlach <d-gerlach@ti.com>

drivers/memory/Makefile.asm-offsets

@@ -1,4 +1,6 @@
-drivers/memory/emif-asm-offsets.s: drivers/memory/emif-asm-offsets.c
+targets += emif-asm-offsets.s
+
+drivers/memory/emif-asm-offsets.s: drivers/memory/emif-asm-offsets.c FORCE
 	$(call if_changed_dep,cc_s_c)
 
 include/generated/ti-emif-asm-offsets.h: drivers/memory/emif-asm-offsets.s FORCE