This patch add elf64 loading support to the elf loader. Since
elf32 and elf64 uses completely different types, to avoid copying all
the code and simply replace elf32 with elf64, use a macro which will
return the appropriate field for each type of header. This macro
generates getter for elf structures according to the class of the loaded
elf.
All direct elf struct dereference are then replaced by call to generated
functions. This allows to keep a common loader code even if types are
different.

Tested-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Clement Leger <cleger@kalray.eu>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>