uprobes/x86: Fix uprobe syscall vs shadow stack

uprobes/x86: Fix uprobe syscall vs shadow stack

The uprobe syscall stores and strips the trampoline stack frame from
the user context, to make it appear similar to an exception at the
original instruction. It then restores the trampoline stack when it
can exit using sysexit.

Make sure to match the regular stack manipulation with shadow stack
operations such that regular and shadow stack don't get out of sync
and causes trouble.

This enables using the optimization when shadow stack is in use.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20250821123657.055790090@infradead.org