docs: include static members in doxygen output

Change-Id: I1867e8d7a3bed1a399c0790f63fee68fb6b299c4
Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>
Reviewed-on: http://openocd.zylin.com/672
Tested-by: jenkins
Reviewed-by: Xiaofan <xiaofanc@gmail.com>

Doxyfile.in

@@ -307,7 +307,7 @@ EXTRACT_PRIVATE        = NO
 # If the EXTRACT_STATIC tag is set to YES all static members of a file
 # will be included in the documentation.
 
-EXTRACT_STATIC         = NO
+EXTRACT_STATIC         = YES
 
 # If the EXTRACT_LOCAL_CLASSES tag is set to YES classes (and structs)
 # defined locally in source files will be included in the documentation.