monitor: Use address_space_read() to read memory

monitor: Use address_space_read() to read memory

Currently monitor.c reads physical memory using
cpu_physical_memory_read(). This effectively hard-codes
assuming that all CPUs have the same view of physical
memory. Switch to address_space_read() instead, which
lets us use the AddressSpace for the CPU we're
reading memory for (falling back to address_space_memory
if there is no CPU, as happens with the "none" board).
As a bonus, this allows us to detect failures to read memory.

Signed-off-by: Peter Maydell <[email protected]>
Reviewed-by: Dr. David Alan Gilbert <[email protected]>
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Message-id: 20181122172653[email protected]