sys_bitfield*(): use 'void *' instead of memaddr_t

Current users of sys_bitfield*() are bending over backwards to cast
what is most of the times a pointer into an integer.

Bitfields can be better described with an void *, so
uint{8,16,32,64}_t or any other container can be used. Most
sys_bitfield*() operations, by extension, can do the same. Note void *
has byte arithmetic, like char *.

This change will also make it implicit, for any future split of the
address space between virtual (what the SW is seeing) and physical
(what the HW is seeing) way clearer, as the functions dealing with
physical, non directly referentiable/mappeable addreses to use an
integer type, like mem_addr_t.

- include/arch/ARCH/*asm_inline*:

  - sys_bitfield*() all modified to take 'void *'

    Note 'void *' arihtmethic is byte based, which makes some things
    easier.

- include/sys_io.h:

  - introduces DEFINE_BITFIELD
  - update docs

- tests/kernel/bitfield: remove all the cast contortions, use DEFINE_BITFIELD
  PENDING: update other TCs

- include/arch/nios/nios2.h, drivers/interrupt_controller/ioapic_intr.c:
  remove cast contortions

Change-Id: I901e62c76af46f26ff0d29cdc37099597f884511
Jira: ZEP-1347
Signed-off-by: Inaky Perez-Gonzalez <inaky.perez-gonzalez@intel.com>