arch: m68k: Implement relocation

Implement relocation for M68K. Perform all the updates in start.S
relocate_code in assemby, since it is a simple matter of traversing
the dynsym table and adding relocation offset - MONITOR_BASE to all
the items in that table. The necessity to deal with MONITOR_BASE is
a specific of M68K, where the ELF entry point is at offset 0x400,
which is the MONITOR_BASE, while TEXT_BASE is at offset 0 .

This also removes the one last user of NEEDS_MANUAL_RELOC, so that
could be finally cleaned up .

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>