ARM: dts: NSP: Add QSPI nodes to NSPI and bcm958625k DTSes

Adding QSPI Device Tree node compatible with the new spi-bcm-qspi driver for
the Broadcom Northstar Plus SoC DTSI and bcm958625k reference board.

Signed-off-by: Kamal Dasu <kdasu.kdev@gmail.com>
Signed-off-by: Yendapally Reddy Dhananjaya Reddy <yendapally.reddy@broadcom.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>