arm64: dts: NS2: convert "ok" to "okay"

Per e-mail from Sergei Shtylyov, the DT spec dictates it should be
"okay" (although "ok" is also recognized).  Thus, changing all "ok" to
"okay" in NS2 device tree files

Suggested-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Jon Mason <jon.mason@broadcom.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>