Introduce generic post-relocation board_r.c

This file handles common post-relocation init for boards which use
the generic framework.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/common/Makefile b/common/Makefile
index a5f5b1a..08af1a8 100644
--- a/common/Makefile
+++ b/common/Makefile
@@ -38,6 +38,7 @@
 
 # boards
 COBJS-$(CONFIG_SYS_GENERIC_BOARD) += board_f.o
+COBJS-$(CONFIG_SYS_GENERIC_BOARD) += board_r.o
 
 # core command
 COBJS-y += cmd_boot.o