ccache: fix ccache-target dependencies

Ccache for the target doesn't make sense without a toolchain, so make
it depend on it.

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

toolchain/ccache/Config.in.2

@@ -2,6 +2,7 @@
 
 config BR2_PACKAGE_CCACHE_TARGET
 	bool "ccache"
+	depends on BR2_PACKAGE_GCC_TARGET
 	help
 	  ccache is a compiler cache. It speeds up recompilation of
 	  C/C++ code by caching previous compiles and detecting when