net: fec: fix regression on i.MX28 introduced by rx_copybreak support

[Lothar Waßmann]

Changes wrt. v1:
- added some cleanup patches
- simplify handling of 'quirks' flags as suggested by Russell King.
- remove DIV_ROUND_UP() from byte swapping loop as suggested by
  Eric Dumazet

Changes wrt. v2:
- rebased against next-20141028
- added some more cleanups in fec.h
- removed unused return value from swap_buffer()
- fixed messed swab32s() call in swap_buffer2()
- fixed messed up setup of fep->quirks