sh: Fix build errors for generic board

This includes the following fixes:
- Define needed __init_end symbol - see initr_reloc_global_data()
- Drop SH-specific struct bd_info
- Add an empty relocate_code() function

This prevents build errors with generic board, but the code will still need
work. Perhaps this is a better alternative than deleting the code.

Signed-off-by: Simon Glass <sjg@chromium.org>