ARM: uniphier: enable CONFIG_SNI_AVE and disable CONFIG_SMC911X

Enable the on-chip ethernet driver for uniphier_{v7,v8}_defconfig.
Disable the on-board SMC911x because it has not migrated to the
driver model yet - it is not possible to enable DM and non-DM
drivers at the same time.

The CONFIG_SMC911X for uniphier_ld4_sld8_defconfig is still kept
because the on-chip ethernet driver for LD4, sLD8 is not supported
yet.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>