openrisc: Add syscall details to emergency syscall debugging

When bringing linux on the or1k Marocchino we ran into issues starting
init.  This patch adds the syscall number and return address to
assist tracing syscalls even before strace is able to be used.

By default this is all disabled but a developer could adjust the ifdef
to enable debugging.

Cc: Andrey Bacherov <bandvig@mail.ru>
Signed-off-by: Stafford Horne <shorne@gmail.com>