sh: Make syscall tracer use tracehook notifiers, add TIF_NOTIFY_RESUME.

This follows the changes in commits:

7d6d637d
4f72c427

on powerpc. Adding in TIF_NOTIFY_RESUME, and cleaning up the syscall
tracing to be more generic. This is an incremental step to turning
on tracehook, as well as unifying more of the ptrace and signal code
across the 32/64 split.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>