SPL crashes when trying to load legacy image from NOR (on MIPS)

[Ezra Buehler]

Since commit 6cc2182c84a ("spl: nor: Don't allocate header on stack")
the MT7688/MIPS-based GARDENA smart Gateway no longer boots. The root
cause seems to be a read of an unaligned 32 bit value from the SPI NOR
flash (image_get_magic() called by spl_parse_image_header()). Before,
having the legacy image header at an unaligned address (directly after
the FDT) was not a problem, because the header was copied to the stack
first.

What is the desired behavior here? Is there some padding needed or
should the problematic code be changed? If so, any suggestions?

Cheers,
Ezra