Documentation: Add cavium SoC and mainboard

* Add documentation for CN81XX SoC
* Add documentation for CN81XX EVB SFF mainboard
* Add documentation for BDK
* Add documentation for BOOTROM and BOOTBLOCK behaviour
* Alphabetically sort vendors

Change-Id: Ibfcd42788e31f684baed658dc3c4dfe1b8e4f354
Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Reviewed-on: https://review.coreboot.org/27150
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: David Hendricks <david.hendricks@gmail.com>
Reviewed-by: Philipp Deppenwiese <zaolin.daisuki@gmail.com>

Documentation/soc/cavium/bootflow.md

@@ -0,0 +1,19 @@
+# Cavium bootflow
+
+The on-chip **BOOTROM** first sets up the L2 cache and the SPI controller.
+It then reads **CSIB_NBL1FW** and **CLIB_NBL1FW** configuration data to get
+the position of the bootstage in flash. It then loads 192KiB from flash into
+L2 cache to a fixed address. The boot mode is called "Non-Secure-Boot" as
+the signature of the bootstage isn't verified.
+The **BOOTROM** can do AES decryption for obfuscation or verify the signature
+of the bootstage. Both features aren't used and won't be described any further.
+
+* The typical position of bootstage in flash is at address **0x20000**.
+* The entry point in physical DRAM is at address **0x100000**.
+
+## Layout
+
+![Bootflow of Cavium CN8xxx SoCs][cavium_bootflow]
+
+[cavium_bootflow]: cavium_bootflow.png
+