Remove recommentation of non-normal mode

Only specify the requirements for `normal` DICE mode and allow vendors
to choose the non-normal mode that fits their need per the ope-dice
specification.

Add a note that RKP required `normal` mode in the DICE chain in order to
trust the device.

Test: n/a
Bug: 263144485
Change-Id: Iaaa3799c53234de61a51ebc855822b93ab3e5bb8