With these you can now do things like:

stm.mem32[0x20000000] = 0x80000000

and read 32-bit values. You can also read all the way to the end
of memory using either stm.mem32[0xfffffffc] or stm.mem32[-4].

IRQs shouldn't use mem32 at all since they'd fail if the top 2 bits
weren't equal, so IRQs should be using 16-bit I/O.