sim: m32r: fixup some of the int<->pointer casts

sim: m32r: fixup some of the int<->pointer casts

The m32r trap code was written for a 32-bit Linux host (and really, one
whose Linux ABI matched pretty exactly).  This has lead to conversions
between integers and pointers which breaks down hard on 64-bit hosts.

Clean up some of the functions where possible to avoid unnecessary
conversions, use uintptr_t to cast 32-bit target pointers to host
pointers in some places, and just stub out a few functions that can't
easily be salvaged currently when sizeof(void*) is not 32-bits.  This
is a bit ugly, but lets us enable warnings for the whole file.