tegra2: Fix out-of-tree build for Ventana.

Since Ventana is derived from Seaboard and requires seaboard.c to build,
make sure board/nvidia/seaboard is created in the build tree.

Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
Acked-by: Stephen Warren <swarren@nvidia.com>
Tested-by: Stephen Warren <swarren@nvidia.com>
Tested-by: Wolfgang Denk <wd@denx.de>

board/nvidia/ventana/Makefile

@@ -25,6 +25,7 @@
 include $(TOPDIR)/config.mk
 
 ifneq ($(OBJTREE),$(SRCTREE))
+$(shell mkdir -p $(obj)../seaboard)
 $(shell mkdir -p $(obj)../common)
 endif