linux-imx

kbuild: remove meaningless 'targets' in ./Kbuild

timeconst.h is generated by $(call filechk,...), missing-syscalls and
old-atomics are invoked by $(call cmd,...)

None of them needs to be added to 'targets'.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>