riotboot: set FLASHFILE to RIOTBOOT_EXTENDED_BIN

... if the riotboot feature is used.

Previously, even an application that had "FEATURES_REQUIRED += riotboot"
set would still flash the non-riotboot binary on "make flash".
This is usualy not what the user wants.

This commit set's the FLASHFILE variable to the combined "riotboot
bootloader + slot0 + empty slot1" binary. This has the effect that make
all, flash and flash-only will compile and/or flash a working riotboot
setup.

tests/riotboot and tests/riotboot_flashwrite now default to flashing the
riotboot-extended binary. tests/riotboot was previously configured to
use the riotboot-combined binary. This has been changed in order to not
behave differently than how usual riotboot applications do.

makefiles/boot/riotboot.mk

@@ -126,6 +126,11 @@ riotboot/slot1: $(SLOT1_RIOT_BIN)
 # Default flashing rule for bootloader + slot 0
 riotboot/flash: riotboot/flash-slot0 riotboot/flash-bootloader
 
+# make applications that use the riotboot feature default to actually using it
+# Target 'all' will generate the combined file directly.
+# It also makes 'flash' and 'flash-only' work without specific command.
+FLASHFILE = $(RIOTBOOT_EXTENDED_BIN)
+
 else
 riotboot:
 	$(Q)echo "error: riotboot feature not selected! (try FEATURES_REQUIRED += riotboot)"

tests/riotboot/Makefile

@@ -18,9 +18,5 @@ DEVELHELP ?= 1
 # Change this to 0 show compiler invocation lines by default:
 QUIET ?= 1
 
-# Target 'all' will generate the combined file directly.
-# It also makes 'flash' and 'flash-only' work without specific command.
-FLASHFILE = $(RIOTBOOT_COMBINED_BIN)
-
 include ../Makefile.tests_common
 include $(RIOTBASE)/Makefile.include