A recent pull-up to the 4.0 branch "improved" the situation somewhat  
(for some random value of "improved"):

  bge0 at pci5 dev 9 function 0: Broadcom BCM5704C Dual Gigabit Ethernet
  bge0: interrupting at ioapic2 pin 0 (irq 11)
-bge0: firmware handshake timed out, val = 4b657654
-bge0: RX CPU self-diagnostics failed!
-bge0: chip initialization failed
+bge0: ASIC BCM5704 A3 (0x2003), Ethernet address 00:e0:81:30:d6:7c
+brgphy0 at bge0 phy 1: BCM5704 1000BASE-T media interface, rev. 0
+brgphy0: using BCM5704 DSP patch
+brgphy0: 10baseT, 10baseT-FDX, 100baseTX, 100baseTX-FDX, 1000baseT,  
1000baseT-FDX, auto
  bge1 at pci5 dev 9 function 1: Broadcom BCM5704C Dual Gigabit Ethernet
  bge1: interrupting at ioapic2 pin 1 (irq 10)
-bge1: firmware handshake timed out, val = 4b657654
-bge1: RX CPU self-diagnostics failed!
-bge1: chip initialization failed
+bge1: ASIC BCM5704 A3 (0x2003), Ethernet address 00:e0:81:30:d6:7d
+brgphy1 at bge1 phy 1: BCM5704 1000BASE-T media interface, rev. 0
+brgphy1: using BCM5704 DSP patch
+brgphy1: 10baseT, 10baseT-FDX, 100baseTX, 100baseTX-FDX, 1000baseT,  
1000baseT-FDX, auto


Trying to use the device results in:

# ifconfig bge0 up
# ifconfig bge1 up
[ after a short while...]
bge0: PHY read timed out
bge0: PHY read timed out
bge0: PHY read timed out
bge0: PHY read timed out
bge0: PHY read timed out
bge1: PHY read timed out
bge0: PHY read timed out
bge0: PHY read timed out
bge1: PHY read timed out
bge1: PHY read timed out
[scrolling quickly....]