doc: Update sysrq doc for sh kgdb trigger.

sh uses the same sysrq trigger as ppc, update the documentation to
reflect that.
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>

Documentation/sysrq.txt

 Linux Magic System Request Key Hacks
 Documentation for sysrq.c
-Last update: 2007-JAN-06
+Last update: 2007-MAR-14
 
 *  What is the magic SysRq key?
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -75,7 +75,7 @@ On all -  write a character to /proc/sysrq-trigger.  e.g.:
 
 'f'	- Will call oom_kill to kill a memory hog process.
 
-'g'	- Used by kgdb on ppc platforms.
+'g'	- Used by kgdb on ppc and sh platforms.
 
 'h'     - Will display help (actually any other key than those listed
           above will display help. but 'h' is easy to remember :-)