A few machines need to translate the ELF header addresses into physical
addresses. Currently the only possibility is to add a value to the
addresses.

This patch replaces the addend argument by and a translation function
and an opaque passed to the function. A NULL function does not translate
the address.

The patch also convert all machines that have an addend, simplify the
PowerPC kernel loading and fix the MIPS kernel loading using this new
feature. Other machines may benefit from this feature.

Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>