Fix allocation of struct in registers on ARM

Fix allocation of struct in registers on ARM

Allocation of struct in core and/or VFP registers on ARM is made by
manipulating the value stack to create 3 distinct zones: parameters
allocated on stack, parameters of type struct allocated in core
registers and parameters of type struct allocated in VFP registers.
Parameters of primitive type can be in any zone. This commit change the
order of the zones from stack, VFP, core to stack, core, VFP (from
highest addresses to lowest ones) in order to correctly deal the
situation when structures are allocated both in core and VFP registers.