Makefile: convert makefiles to Kbuild style and delete grep switch

We have converted all makefiles needed to build $(LIBS).

Until this commit we used to grep switch so that U-Boot style
and Kbuild style makefiles coexist.
But we do not need any more.

Goint forward, use always Kbuild style Makefile when adding
a new Makefile

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>