ARM: dts: K2G: Add support for QSPI controller

K2G SoC has a Cadence QSPI controller to communicate with NOR flash
devices. Add DT nodes to support the same.
Also, K2G EVM has a s25fl512s flash connect to QSPI bus at CS 0. Add nor
flash slave node for the same.

Signed-off-by: Vignesh R <vigneshr@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Jagan Teki <jteki@openedev.com>