Add iso_image option to enable/disable building of iso images

make flashfiles takes long time.

In order to reduce image generation time provided option to skip
building of ISO image. If user wants to skip building of ISO image
make command to use is "make flashfiles iso_image=false"

Tracked-On: OAM-111036
Signed-off-by: Chen, Gang G <gang.g.chen@intel.com>

tasks/flashfiles.mk

@@ -399,6 +399,7 @@ publish_ifwi:
 	@echo "Warning: Unable to fulfill publish_ifwi makefile request"
 endif
 
+ifneq ($(iso_image),false)
 	@echo "Generating ISO image $(ISO_INSTALL_IMG) ...";
 	$(hide)rm -rf $(PRODUCT_OUT)/efi_images_tmp/;
 	$(hide)rm -rf $(ISO_INSTALL_IMG) $(ISO_INSTALL_IMG_ZIP)
@@ -462,6 +463,7 @@ endif
 	$(hide) cp -r $(ISO_INSTALL_IMG_ZIP) $(TOP)/pub/$(TARGET_PRODUCT)/$(TARGET_BUILD_VARIANT)
 
 	$(hide)rm -rf $(PRODUCT_OUT)/efi_images_tmp/ $(PRODUCT_OUT)/iso $(ISO_EFI)
-	$(hide)rm -rf $(TOP)/$(TARGET_PRODUCT)-releasefiles-$(TARGET_BUILD_VARIANT).tar.gz && rm -rf $(TOP)/Release_Files && rm -rf $(TOP)/$(TARGET_PRODUCT)-flashfiles-*.zip && rm -rf $(TOP)/scripts && rm -rf $(TOP)/*patches && rm -rf $(TOP)/*provisioning && rm -rf $(TOP)/pub/$(TARGET_PRODUCT)/$(TARGET_BUILD_VARIANT)/Release_Files $(TOP)/*-flashfile-*.iso
 
 	@echo "ISO Release files are published"
+endif
+	$(hide)rm -rf $(TOP)/$(TARGET_PRODUCT)-releasefiles-$(TARGET_BUILD_VARIANT).tar.gz && rm -rf $(TOP)/Release_Files && rm -rf $(TOP)/$(TARGET_PRODUCT)-flashfiles-*.zip && rm -rf $(TOP)/scripts && rm -rf $(TOP)/*patches && rm -rf $(TOP)/*provisioning && rm -rf $(TOP)/pub/$(TARGET_PRODUCT)/$(TARGET_BUILD_VARIANT)/Release_Files $(TOP)/*-flashfile-*.iso