UEC: Fix compiler warnings introduced by linux/mii.h change

Patch 8ef583a0 [miiphy: convert to linux/mii.h] introduced the following
compiler warnings in the uec ethernet driver:

In file included from /local/home/galak/git/u-boot-85xx/include/miiphy.h:37:0,
                 from uec.c:32:
/local/home/galak/git/u-boot-85xx/include/linux/mii.h:133:0: warning: "LPA_1000FULL" redefined
uec_phy.h:34:0: note: this is the location of the previous definition
/local/home/galak/git/u-boot-85xx/include/linux/mii.h:134:0: warning: "LPA_1000HALF" redefined
uec_phy.h:35:0: note: this is the location of the previous definition
In file included from /local/home/galak/git/u-boot-85xx/include/miiphy.h:37:0,
                 from uec_phy.c:27:
/local/home/galak/git/u-boot-85xx/include/linux/mii.h:133:0: warning: "LPA_1000FULL" redefined
uec_phy.h:34:0: note: this is the location of the previous definition
/local/home/galak/git/u-boot-85xx/include/linux/mii.h:134:0: warning: "LPA_1000HALF" redefined
uec_phy.h:35:0: note: this is the location of the previous definition

Fix them be removing the duplication in the uec code and utlizing the
linux/mii.h version instead.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>