include: arch: move bits_portable.h to arch/common

We had architectures doing this differently, some had a dedicated
sys_io.h file, some not. Unify how it is done by splitting the arch
specific sys_io implementation into a sys_io file and include it
instead.

Move bits_portable.h to arch/common and split the file so more
architecture can reuse some of the definitions here instead of
duplicating code.

Where applicable use the common sys_io/ffs definitions.

Signed-off-by: Anas Nashif <anas.nashif@intel.com>