ARM: set --be8 when linking modules

To avoid having to make every text section swap the instruction order
of all instructions, make sure modules are built also built with --be8
(as is the current kernel final link).

If we do not do this, we would end up having to swap all instructions
when loading a module, instead of just the instructions that we are
applying ELF relocations to.

Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Reviewed-by: Dave Martin <Dave.Martin@arm.com>