net: ethernet: bgmac: init sequence bug

Fix a bug in the 'bgmac' driver init sequence that blind writes for init
sequence where it should preserve most bits other than the ones it is
deliberately manipulating.

The code now checks to see if the adapter needs to be brought out of
reset (where as before it was doing an IDM write to bring it out of
reset regardless of whether it was in reset or not).  Also, removed
unnecessary usleeps (as there is already a read present to flush the
IDM writes).

Signed-off-by: Zac Schroff <zschroff@broadcom.com>
Signed-off-by: Jon Mason <jon.mason@broadcom.com>
Fixes: f6a95a24 ("net: ethernet: bgmac: Add platform device support")
Signed-off-by: David S. Miller <davem@davemloft.net>