x86: Add error checking to x86 relocation code

This does not actually change normal behaviour, but adds a check that
should detect corruption of relocation data (e.g. by using BSS data
prior to relocation).

Also add additional debugging output when enabled.

During this investigation, two situations have been seen:
1. calculate_relocation_address():
	uintptr_t size = (uintptr_t)&__bss_end - (uintptr_t)&__text_start;

turns into
     111166f:	b8 83 c4 17 01       	mov    $0x117c483,%eax

whih is beyond the end of bss:

0117b484 g       .bss	00000000 __bss_end

Somehow the __bss_end here is 255 bytes ahead.

2. do_elf_reloc_fixups():

	uintptr_t size = (uintptr_t)&__bss_end - (uintptr_t)&__text_start;

Here the __text_start is 0 in the file:

 1111d9f:	bb a0 e0 13 01       	mov    $0x113e0a0,%ebx
1111da4:	81 ef 00 00 00 00    	sub    $0x0,%edi

As it happens, both of these are in pre-relocation code.

For these reasons we silent check and ignore bad relocations.

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