Documentation: Move firmware flashing tutorial to tutorial section

There is no need that the tutorial for flashing firmware has its own
point in the main menu. Thus, move it to the tutorial section.

Change-Id: Ife6d97254af4c006fe01480a78c76303f9cb34bb
Signed-off-by: Felix Singer <felixsinger@posteo.net>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/62424
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Thomas Heijligen <src@posteo.de>

Documentation/mainboard/supermicro/x10slm-f.md

@@ -42,7 +42,7 @@ Now, run `make` to build the coreboot image.
 
 ```eval_rst
 In addition to the information here, please see the
-:doc:`../../flash_tutorial/index`.
+:doc:`../../tutorial/flashing_firmware/index`.
 ```
 
 ### Internal programming

Documentation/mainboard/supermicro/x11-lga1151-series/x11-lga1151-series.md

@@ -56,6 +56,6 @@ These issues apply to all boards. Have a look at the board-specific issues, too.
 [Supermicro X11 LGA1151 series]: https://www.supermicro.com/products/motherboard/Xeon3000/#1151
 [OpenBMC]: https://www.openbmc.org/
 [flashrom]: https://flashrom.org/Flashrom
-[flashing tutorial]: ../../../../flash_tutorial/ext_power.md
+[flashing tutorial]: ../../../../tutorial/flashing_firmware/ext_power.md
 [Intel FSP2.0]: ../../../../soc/intel/fsp/index.md
 [AST2400]: https://www.aspeedtech.com/products.php?fPath=20&rId=376

Documentation/mainboard/supermicro/x9sae.md

@@ -105,4 +105,4 @@ seems that it shall not appear on X9SAE even if it is defined.
 [X9SAE-V]:  https://www.supermicro.com/products/motherboard/xeon/c216/x9sae-v.cfm
 [W25Q128FVSG]: https://static.chipdip.ru/lib/093/DOC001093213.pdf
 [flashrom]: https://flashrom.org/Flashrom
-[flash internally]: ../../flash_tutorial/int_flashrom.md
+[flash internally]: ../../tutorial/flashing_firmware/int_flashrom.md