Makefile: clean image.map

binman tools for creating single image build will create image.map
at the end, which has information about binman image node details.

current u-boot, is unable to clean this image.map so add a command
entry in clean target in Makefile.
Signed-off-by: NJagan Teki <jagan@amarulasolutions.com>
Reviewed-by: NKever Yang <kever.yang@rock-chips.com>

Makefile

@@ -1847,7 +1847,8 @@ clean: $(clean-dirs)
 		-o -name modules.builtin -o -name '.tmp_*.o.*' \
 		-o -name 'dsdt.aml' -o -name 'dsdt.asl.tmp' -o -name 'dsdt.c' \
 		-o -name '*.efi' -o -name '*.gcno' -o -name '*.so' \) \
-		-type f -print | xargs rm -f
+		-type f -print | xargs rm -f \
+		image.map
 
 # mrproper - Delete all generated files, including .config
 #