e1000: Trivial implementation of various MAC registers

e1000: Trivial implementation of various MAC registers

These registers appear in Intel's specs, but were not implemented.
These registers are now implemented trivially, i.e. they are initiated
with zero values, and if they are RW, they can be written or read by the
driver, or read only if they are R (essentially retaining their zero
values). For these registers no other procedures are performed.

For the trivially implemented Diagnostic registers, a debug warning is
produced on read/write attempts.

PLEASE NOTE: these registers will not be active, nor will migrate, until
a compatibility flag will be set (in a later patch in this series).

The registers implemented here are:

Transmit:
RW: AIT

Management:
RW: WUC     WUS     IPAV    IP6AT*  IP4AT*  FFLT*   WUPM*   FFMT*   FFVT*

Diagnostic:
RW: RDFH    RDFT    RDFHS   RDFTS   RDFPC   PBM*    TDFH    TDFT    TDFHS
    TDFTS   TDFPC

Statistic:
RW: FCRUC
R:  RNBC    TSCTFC  MGTPRC  MGTPDC  MGTPTC  RFC     RJC     SCC     ECOL
    LATECOL MCC     COLC    DC      TNCRS   SEC     CEXTERR RLEC    XONRXC
    XONTXC  XOFFRXC XOFFTXC

Signed-off-by: Leonid Bloch <leonid.bloch@ravellosystems.com>
Signed-off-by: Dmitry Fleytman <dmitry.fleytman@ravellosystems.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>