cappuccino/fetch: generate NOPs on reset and pipeline flush
decode: generate jal result
cappuccino: use jal result from decode

instead of generating it in wb stage
decode: seperate decode and execute rfd_adr signals

This is a preparation for moving cappuccino's branch
resolving into decode stage.
It also rename the rfa_adr and rfb_adr signals with the
decode prefix.
decode: rename exec_bubble_o to execute_bubble_o

let's keep the stage prefixes consistant
decode: clear execute_bubble_o on pipeline flush
decode: whitespace fix
cappuccino/rf: rename exec_ prefix to execute_
cappuccino/rf: add decode_ prefix to rfX_adr signals
cappuccino/rf: add execute_ prefix to rfX_o signals
decode: declare wires individually
decode: stall fetch stage during rfe (by asserting decode_bubble)