Use 'E' instead of 'X' for unsigned module taint flag.

Takashi Iwai <tiwai@suse.de> says:
> The letter 'X' has been already used for SUSE kernels for very long
> time, to indicate the external supported modules.  Can the new flag be
> changed to another letter for avoiding conflict...?
> (BTW, we also use 'N' for "no support", too.)

Note: this code should be cleaned up, so we don't have such maps in
three places!

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

Documentation/oops-tracing.txt

@@ -265,7 +265,7 @@ characters, each representing a particular tainted value.
 
  13: 'O' if an externally-built ("out-of-tree") module has been loaded.
 
- 14: 'X' if an unsigned module has been loaded in a kernel supporting
+ 14: 'E' if an unsigned module has been loaded in a kernel supporting
      module signature.
 
 The primary reason for the 'Tainted: ' string is to tell kernel