MEM: Unify bus access methods and prepare for master/slave split

MEM: Unify bus access methods and prepare for master/slave split

This patch unifies the recvFunctional, recvAtomic and recvTiming to
all be based on a similar structure: 1) extract information about the
incoming packet, 2) send it out to the appropriate snoopers, 3)
determine where it is going, and 4) forward it to the right
destination. The naming of variables across the different access
functions is now consistent as well.

Additionally, the patch introduces the member functions releaseBus and
retryWaiting to better distinguish between the two cases when we
should tell a sender to retry. The first case is when the bus goes
from busy to idle, and the second case is when it receives a retry
from a destination that did not immediatelly accept a packet.

As a very minor change, the MMU debug flag is no longer used in the bus.