ARM: socfpga: Fix A10 SoCDK Kconfig

ARM: socfpga: Fix A10 SoCDK Kconfig

The Kconfig checked for SoCFPGA Arria10 as a platform, instead of
checking for specific board configuration, which works with one
single platform in tree, but not with multiple. Fix it.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Chin Liang See <chin.liang.see@intel.com>
Cc: Dinh Nguyen <dinguyen@kernel.org>
Cc: Simon Goldschmidt <simon.k.r.goldschmidt@gmail.com>
Cc: Tien Fong Chee <tien.fong.chee@intel.com>