net: mvgbe: Fix build error with CONFIG_PHYLIB

net: mvgbe: Fix build error with CONFIG_PHYLIB

Commit 5a49f17481bb ("net: mii: Use spatch to update miiphy_register")
updated the mvgbe implementation of smi_reg_read/smi_reg_write. Prior to
that change mvgbe_phy_read and mvgbe_phy_write where used as wrappers to
satisfy the phylib APIs. Because these functions weren't updated in that
commit build errors where triggered when CONFIG_PHYLIB was enabled.

Fix these build errors by removing mvgbe_phy_read and mvgbe_phy_write
and using smi_reg_read/smi_reg_write directly.

Signed-off-by: Chris Packham <judge.packham@gmail.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>