mpm: n3xx: Allow to run without daughterboards connected

The product ID will fall back to the motherboard ID (n300, n310). This
will load FPGA images even if there is no daughterboard connected.

Author: Trung Tran

mpm/python/usrp_mpm/periph_manager/n3xx.py

@@ -92,7 +92,9 @@ class n3xx(ZynqComponents, PeriphManagerBase):
     # manager class. The format of this map is:
     # (motherboard product code, (Slot-A DB PID, [Slot-B DB PID])) -> product
     product_map = {
+        ('n300', tuple()) : 'n300',
         ('n300', (MG_PID,       )): 'n300', # Slot B is empty
+        ('n310', tuple()) : 'n310',
         ('n310', (MG_PID, MG_PID)): 'n310',
         ('n310', (MG_PID,       )): 'n310', # If Slot B is empty, we can
                                             # still use the n310.bin image.