ARM: rmobile: Introduce weak default board_init()

Introduce weak default board_init() in rcar-common/common.c , which
allows complete removal of ebisu.c and condor.c at the same time .

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
diff --git a/board/renesas/ebisu/Makefile b/board/renesas/ebisu/Makefile
index 1fd9a03..956ce8a 100644
--- a/board/renesas/ebisu/Makefile
+++ b/board/renesas/ebisu/Makefile
@@ -9,5 +9,5 @@
 ifdef CONFIG_SPL_BUILD
 obj-y	:= ../rcar-common/gen3-spl.o
 else
-obj-y	:= ebisu.o ../rcar-common/common.o
+obj-y	:= ../rcar-common/common.o
 endif