Fix handling of long argument spanning register/memory.

Comment in arm_lir.h says:
 * If a 64-bit argument would span the register/memory argument
 * boundary, it will instead be fully passed in the frame.

This change implements such logic for all platforms. We still need
to pass the low part in register as well because I haven't ported
the jni compilers (x86 and mips) to it.

Once the jni compilers are updated, we can remove the register
assignment.

Note that this greatly simplifies optimizing's register allocator
by not having to understand a long spanning register and memory.

Change-Id: I59706ca5d47269fc46e5489ac99bd6576e87e7f3