kernel: remove duplicate #define's in at803x Ethernet PHY driver

kernel: remove duplicate #define's in at803x Ethernet PHY driver

AT803X_REG_CHIP_CONFIG and AT803X_BT_BX_REG_SEL have been defined
upstream by commit f62265b53ef3 ("at803x: double check SGMII side autoneg")
An existing local patch then added those exact same defines again which
isn't necessary, so remove them.

Fixes: f791fb4af450 ("kernel: add linux 4.9 support")
Fixes: b3f95490b9be ("kernel: generic: Add kernel 4.14 support")
Signed-off-by: Daniel Golle <daniel@makrotopia.org>
(cherry picked from commit 67fcff6aaf)