Add more comments to rings supported by the controller. Different

Add more comments to rings supported by the controller. Different
versions of controller support different number of ring control
blocks such that adjust code a bit to access known number of
send/receive ring control blocks. Previously bge(4) blindly
accessed 16 send/receive RCBs. Also move initializing standard
receive producer ring producer index, jumbo receive producer ring
producer index and mini receive producer ring producer index to
the end of each receive producer ring initialization.

Do not assume mini receive producer ring is available only when
controller has jumbo frame capability, instead explicitly check
ASIC version BCM5700 to disable mini receive producer ring.

Additionally always enable send ring 0 regardless of controller
versions. Previously bge(4) didn't enable send ring 0 if controller
is BGE_IS_5705_PLUS. Becase bge(4) need 1 send ring to send frames
at least, I have no idea how it would have worked so far.

Submitted by:	davidch