eco32: traps: handle illegal instructions

Send an SIGILL signal upon illegal instructions in user space.

Signed-off-by: Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>
eco32: rework the pagefault handling path

Let the pagefaults be dispatched by do_exception to consolidate
the asm code for the exceptions slow path.

Signed-off-by: Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>