ARM: dts: socfpga: Fix up button mapping on VINING FPGA

Add missing buttons and signals to the VINING FPGA device tree,
so they are presented to the userspace via gpio-keys evdev.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Dinh Nguyen <dinguyen@kernel.org>
Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>