realtek: Use MDIO_* constants from <linux/mdio.h>

realtek: Use MDIO_* constants from <linux/mdio.h>

To improve code readability in drivers/net/phy/rtl83xx-phy.c, replace
constants MMD_AN and MMD_VEND2 from drivers/net/phy/rtl83xx-phy.h with
MDIO_MMD_AN and MDIO_MMD_VEND2 from <linux/mdio.h>.

Also, replace
BIT(0) with MDIO_EEE_2_5GT,
BIT(1) with MDIO_EEE_100TX,
BIT(2) with MDIO_EEE_1000T,
BIT(9) with MDIO_AN_CTRL1_RESTART,
BIT(12) with MDIO_AN_CTRL1_ENABLE,
32 with MDIO_AN_10GBT_CTRL,
60 with MDIO_AN_EEE_ADV, and
62 with MDIO_AN_EEE_ADV2
from <linux/mdio.h>.

Suggested-by: DENG Qingfang <dqfext@gmail.com>
Signed-off-by: Pascal Ernster <git@hardfalcon.net>