image: Move HOSTCC image code to tools/

This code is never compiled into U-Boot, so move it into a separate
file in tools/ to avoid the large #ifdef.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Marek Vasut <marex@denx.de>

tools/Makefile

@@ -96,6 +96,7 @@ NOPED_OBJ_FILES-y += aisimage.o
 NOPED_OBJ_FILES-y += kwbimage.o
 NOPED_OBJ_FILES-y += pblimage.o
 NOPED_OBJ_FILES-y += imximage.o
+NOPED_OBJ_FILES-y += image-host.o
 NOPED_OBJ_FILES-y += omapimage.o
 NOPED_OBJ_FILES-y += mkenvimage.o
 NOPED_OBJ_FILES-y += mkimage.o
@@ -212,6 +213,7 @@ $(obj)mkimage$(SFX):	$(obj)aisimage.o \
 			$(obj)fit_image.o \
 			$(obj)image-fit.o \
 			$(obj)image.o \
+			$(obj)image-host.o \
 			$(obj)imximage.o \
 			$(obj)kwbimage.o \
 			$(obj)pblimage.o \