* Add dpu_tty.py
* Add dpu_tty.py to scripts

Signed-off-by: Wenchung Wang vincwang@cisco.com

What I did

Add DPU TTY console utility.

How I did it

* Read platform.json to retrieve TTY settings in DPUS section. Set up TTY
console according to TTY device name and baud rate.
* Also provide options to overwrite default TTY device and baud rate.

'''
"DPUS": {
    "dpu0": {
        "serial-console": {
            "device": "ttyS4",
            "baud-rate": "115200"
        }
    },
    "dpu1": {
        "serial-console": {
            "device": "ttyS5",
            "baud-rate": "115200"
        }
    }
},
'''

How to verify it

Run the utility on a smart switch that provides DPU UART console via
ttyS device. The test plan is at
https://github.com/sonic-net/sonic-mgmt/pull/12701/files section 1.4.

Add DPU serial console utility.