Provide selfboot() external declaration in a common file

The earlier compilation warning fix (7e4aa17) incorrectly assumed that
selfboot() is a function defined in the cbfs driver. This is a
commonly available function, it should not come from cbfs.h.

BUG=none
TEST=the following command succeeds:
  $ for b in rambi storm nyan_big; do
       cros_workon-$b start libpayload
       emerge-$b libpayload || break
     done

Change-Id: I3ef49d849168ad9dc24589cbd9ce7382052345bd
Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/201386

payloads/libpayload/include/cbfs.h

@@ -81,9 +81,6 @@ void *cbfs_simple_buffer_unmap(struct cbfs_simple_buffer *buffer,
 // Utility functions
 int run_address(void *f);
 
-/* Defined in src/lib/selfboot.c */
-void selfboot(void *entry);
-
 /* Defined in individual arch / board implementation. */
 int init_default_cbfs_media(struct cbfs_media *media);
 

payloads/libpayload/include/libpayload.h

@@ -60,9 +60,6 @@
 #ifdef CONFIG_LP_LAR
 #include <lar.h>
 #endif
-#ifdef CONFIG_LP_CBFS
-#include <cbfs.h>
-#endif
 
 #define MIN(a,b) ((a) < (b) ? (a) : (b))
 #define MAX(a,b) ((a) > (b) ? (a) : (b))
@@ -445,4 +442,7 @@ char *readline(const char *prompt);
 int getline(char *buffer, int len);
 /** @} */
 
+/* Defined in arch/${ARCH}/selfboot.c */
+void selfboot(void *entry);
+
 #endif