boards: nxp: add documentation for SEGGER SystemView support with ECC

SOCs using ECC require the SEGGER RTT control block address to be
provided to the tooling, as the SEGGER tools will not scan the memory
range of ECC ram. Add documentation making this clear to boards with
these SOCs.

Signed-off-by: Daniel DeGrasse <daniel.degrasse@nxp.com>