Dummy instruction fixes
Created by: silabs-oysteink
Added forwarding of x0 from dummies writing x0 to dummies reading x0. No cross forwarding between dummies and regular instructions, and no forwarding of x0 between regular instructions.
Fixed bug where the x0 flops for dummies would be reset to 0 if no dummy was in WB.
Signed-off-by: Oystein Knauserud Oystein.Knauserud@silabs.com