dt: mimxrt700_evk/hifi4: Add definitions

Add dummy interrupt controller, clock control, pin control, Flexcomm 0,
Flexcomm 2, SAI0, SAI1, SAI2 into SoC's DT. Enable relevant nodes in
board's DT and include pinctrl definitions. Add default LED and button
nodes. Set /hifi4's real frequency. Add memory nodes for device's main
SRAM.

Signed-off-by: Vit Stanicek <vit.stanicek@nxp.com>