ARM: mxs: remove obsolete startup code for TX28

The power and reset handling of the FEC ethernet driver is sufficient
to get the ethernet PHY on the TX28 into a usable state.
Remove the code that does the PHY initialization on startup.

Signed-off-by: Lothar Waßmann <LW@KARO-electronics.de>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>