cleanup: include/: move sys_io.h to sys/sys_io.h

move sys_io.h to sys/sys_io.h and
create a shim for backward-compatibility.

No functional changes to the headers.
A warning in the shim can be controlled with CONFIG_COMPAT_INCLUDES.

Related to #16539

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