kernel: Use full user defined path to ccache

The built ccache command is now deprecated and spits out errors. ccache is
also no longer used for the full build unless CCACHE_EXEC is defined. Move
the kernel to the same logic in order to actually use ccache and silence
the warnings.

Change-Id: Iccedd9d5868d31060677667cc18810aae0149a26
1 file changed