.bss __rel_start (OVERLAY) was used to optimize RAM size used by
barebox. Since .bss and __rel_start overlap, we should clear bss only
after __rel_start was used. Following patch changed initialization
sequence to clear .bss before __rel_start:
1e5aef61fc6a444 ("MIPS: reloc: init bss and cpu")

This make relocation buffer unusable and broke relocation with different
symptoms reported by Antony Pavlov <antonynpavlov@gmail.com>:
  * iomem output has no information on sdram regions, so memtest is unusable;
  * pc = 0xa081232c, relocation does not work, barebox is located with 8M offset
    from start of RAM. The board has 256M and relocation routine
    should move barebox code much higher;
  * pc = 0xa081232c, so barebox code works from KSEG1 not from KSEG0 as MMU=y option implies.

There is a choice of moving .bss clear sequence after __rel_start or
remove this optimization. Since the use of this optimization is minimal
and danger to trap in to similar issue is still high, i prefer to remove
this optimization.

As result of this change, we need to fix calculation of relocation are
size:
relocate_code() calculates relocation area size as a sum (barebox_image_size +
bss_len). barebox_image_size and bss_len are calculated as (__image_end -
__image_start) and (__bss_stop - __bss_start) respectively. This doesn't take
into account relocation data placed between  __image_end and __bss_start.
However relocation preserves BSS position relative to image start, as if
relocation data is still there. This causes RAM overflow during BSS
initialization in main_entry(). This problem may be hidden due to the alignment
of the `relocaddr`.

Reported-by: Antony Pavlov <antonynpavlov@gmail.com>
Fixes: 1e5aef61fc6a444 ("MIPS: reloc: init bss and cpu")
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Peter Mamonov <pmamonov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>