ARM: rmobile: Replace CONFIG_RAVB with CONFIG_RENESAS_RAVB in boards

The configuration option name is the later, so replace usage of
CONFIG_RAVB in board files with CONFIG_RENESAS_RAVB , otherwise
the RAVB pinmux is not set and ethernet does not work.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
Signed-off-by: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>