Documentation: add missing tainted bits to Documentation/sysctl/kernel.txt

Two of the bits in the tainted flag are not documented.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/sysctl/kernel.txt

@@ -601,6 +601,8 @@ can be ORed together:
         instead of using the one provided by the hardware.
  512 - A kernel warning has occurred.
 1024 - A module from drivers/staging was loaded.
+2048 - The system is working around a severe firmware bug.
+4096 - An out-of-tree module has been loaded.
 
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