Prior to this change machine.mem32['foo'] (or using any other non-integer
subscript) could result in a fault due to 'foo' being interpreted as an
integer. And when writing code it's hard to tell if the fault is due to a
bad subscript type, or an integer subscript that specifies an invalid
memory address.
The type of the object used in the subscript is now tested to be an
integer by using mp_obj_get_int_truncated instead of
mp_obj_int_get_truncated. The performance hit of this change is minimal,
and machine.memX objects are more for convenience than performance (there
are many other ways to read/write memory in a faster way),
Fixes issue #6588.
This requires root access. And on recent Linux kernels, with
CONFIG_STRICT_DEVMEM option enabled, only address ranges listed in
/proc/iomem can be accessed. The above compiled-time option can be
however overriden with boot-time option "iomem=relaxed".
This also removed separate read/write paths - there unlikely would
be a case when they're different.
