How to config ENV_IS_IN_NAND to default option in Kconfig?

[天田南]

Hi all:

I'm intend to set ENV_IS_IN_NAND to my default option in env/Kconfig.
I can see the ENV_IS_IN_NAND is depends on !CHAIN_OF_TRUST,
but I don't know where CHAIN_OF_TRUST is configured from.
So where should I define this CHAIN_OF_TRUST in Kconfig?
And What does CHAIN_OF_TRUST do?

Thanks
Amada.Minami