Change MUL shift input to rank 1 & fix MUL operation

Align shift input to specification - rank 1 not rank 0.
Change to using const as the default for the shift input.
Align MUL reference code to pseudo code in spec.
Update example LSTM test.

Fix rank 0 data output to be rank 0 (instead of rank 1).

Signed-off-by: Jeremy Johnson <jeremy.johnson@arm.com>
Change-Id: Ic9cdb0e50f0b01c9e7c446b2642586fd74e85ca0