boards: nxp: frdm_mcxn947: doc fixes

- fix schematic link pointing to different board
- fix link to the board_defconfig file
- remove the "Debug Firmware" link that was not referenced anywhere
- add a link to the board user manual
- minor additions to the debug with J-Link section

Signed-off-by: Thomas Stranger <thomas.stranger@outlook.com>
1 file changed