stmmac: intel: move definitions to dwmac-intel header file

Currently some of the dwmac-intel definitions are in the header file,
while some are in the driver source file. Cleaning this by moving all
the definitions to the header file.

Signed-off-by: Wong Vee Khee <vee.khee.wong@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>