FROMLIST: arm64: disable function graph tracing with SCS

The graph tracer hooks returns by modifying frame records on the
(regular) stack, but with SCS the return address is taken from the
shadow stack, and the value in the frame record has no effect. As we
don't currently have a mechanism to determine the corresponding slot
on the shadow stack (and to pass this through the ftrace
infrastructure), for now let's disable the graph tracer when SCS is
enabled.

Bug: 145210207
Change-Id: I65dd098be827121ecf0c08538b11e3b98f5eacde
(am from https://lore.kernel.org/patchwork/patch/1149057/

)
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>