This commit fixes an issue that would cause the L2P DMA to drop some data when the WB slave would
stall at the same cycle as the dual-clock FIFO would raise the 'full' flag.

The WB state machine has been redesigned in order to solve this issue and make sure that data is
properly retained when this condition appears.

Signed-off-by: Dimitris Lampridis <dimitris.lampridis@cern.ch>