e1000: remove duplicated phy codes

Add two files base.c and base.h to reduce the redundancy
in the silicon family code.
Remove the code duplication from e1000_82575 files.
Clean family specific functions from base.
Fix up a stray and duplicate function declaration.

Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: Sasha Neftin <sasha.neftin@intel.com>
Signed-off-by: Guinan Sun <guinanx.sun@intel.com>
Reviewed-by: Wei Zhao <wei.zhao1@intel.com>

Approved by:	imp
Obtained from:	DPDK (44dddd14059f151f39f7e075b887decfc9a10f11)
MFC after:	1 week

(cherry picked from commit 6b9d35f)

sys/conf/files

@@ -1691,6 +1691,8 @@ dev/e1000/e1000_i210.c		optional em \
 	compile-with "${NORMAL_C} -I$S/dev/e1000"
 dev/e1000/e1000_api.c		optional em \
 	compile-with "${NORMAL_C} -I$S/dev/e1000"
+dev/e1000/e1000_base.c		optional em \
+	compile-with "${NORMAL_C} -I$S/dev/e1000"
 dev/e1000/e1000_mac.c		optional em \
 	compile-with "${NORMAL_C} -I$S/dev/e1000"
 dev/e1000/e1000_manage.c	optional em \