arm: socfpga: av_socdk: Add support for QSPI boot

Add missing DT nodes to allow booting from QSPI NOR.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Dinh Nguyen <dinguyen@opensource.altera.com>
Cc: Chin Liang See <clsee@altera.com>
Cc: Denis Bakhvalov <denis.bakhvalov@nokia.com>