common: Move jumptable_init() out of common.h

This function is defined in exports.c so move it to its header file.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/common/board_r.c b/common/board_r.c
index e7c2594..2f5e534 100644
--- a/common/board_r.c
+++ b/common/board_r.c
@@ -12,6 +12,7 @@
 #include <common.h>
 #include <api.h>
 #include <cpu_func.h>
+#include <exports.h>
 #include <irq_func.h>
 #include <u-boot/crc.h>
 /* TODO: can we just include all these headers whether needed or not? */