tools: do not apply ccache dependency to xz

Since XZ is needed to bootstrap building ccache we must not depend on it,
so remove the dependency on ccache to avoid circular dependencies.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

tools/Makefile

@@ -89,7 +89,7 @@ ifneq ($(HOST_OS),Linux)
 endif
 
 ifneq ($(CONFIG_CCACHE)$(CONFIG_SDK),)
-$(foreach tool, $(filter-out patch,$(tools-y)), $(eval $(curdir)/$(tool)/compile += $(curdir)/ccache/install))
+$(foreach tool, $(filter-out xz patch,$(tools-y)), $(eval $(curdir)/$(tool)/compile += $(curdir)/ccache/install))
 tools-y += ccache
 endif