ARM: socfpga: move CONFIG_BOOTDELAY to Kconfig for IS1 board

This recently added board missed the tree-wide migration of
CONFIG_BOOTDELAY.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Pavel Machek <pavel@denx.de>
Reviewed-by: Heiko Schocher <hs@denx.de>
Reviewed-by: Stefan Roese <sr@denx.de>