image: fix device profile specific COMPILE targets

Commit a01d23e75 ("image: always rebuild kernel loaders")
is a step in the right direction, but exposed some issues
and regressions in the makefile.

Some of the files made by device specific COMPILE targets
start with an "append" command (i.e. >> instead of > redirection)
and if the file already exists, the target file is the
input to itself before the first recipe-specified input.

Fixes: a01d23e75 ("image: always rebuild kernel loaders")
Fixes: a7fb589e8 ("image: always rebuild kernel loaders")
Signed-off-by: Michael Pratt <mcpratt@pm.me>

include/image.mk

@@ -520,6 +520,7 @@ define Device/Build/compile
   $$(_COMPILE_TARGET): $(KDIR)/$(1)
   $(eval $(call Device/Export,$(KDIR)/$(1)))
   $(KDIR)/$(1): FORCE
+	rm -f $(KDIR)/$(1)
 	$$(call concat_cmd,$(COMPILE/$(1)))
 
 endef