net: MVGBE don't automatically select PHYLIB

When Kconfig support was added for MVGBE it included automatically
selected PHYLIB support. But MVGBE does not need PHYLIB it will build
fine without it. Commit ed52ea50 ("net: add Kconfig for MVGBE")
should have been a no-op in terms of build size but because of the
selecting PHYLIB the openrd configs increased in size.

Remove the automatic selection of PHYLIB, boards that need it will have
already enabled it in their config header file.

Fixes: commit ed52ea50 ("net: add Kconfig for MVGBE")
Signed-off-by: Chris Packham <judge.packham@gmail.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
Signed-off-by: Stefan Roese <sr@denx.de>