linux-user: Make semihosting heap/stack fields abi_ulongs

linux-user: Make semihosting heap/stack fields abi_ulongs

The fields in the TaskState heap_base, heap_limit and stack_base
are all guest addresses (representing the locations of the heap
and stack for the guest binary), so they should be abi_ulong
rather than uint32_t. (This only in practice affects ARM AArch64
since all the other semihosting implementations are 32-bit.)

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Laurent Desnogues <laurent.desnogues@gmail.com>
Message-id: 1466783381-29506-2-git-send-email-peter.maydell@linaro.org