sh: ftrace: Fix up syscall tracepoint support.

Sync up with latest core changes in the syscalls tracing area:

- tracing: Map syscall name to number (syscall_name_to_nr())
- tracing: Call arch_init_ftrace_syscalls at boot
- tracing: add support tracepoint ids (set_syscall_{enter,exit}_id())

Taken from the s390 change.

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