remove vx900_int16 doxygen module/group

This doxygen directive was creating a top level modules section, which
had the vx900_int15 code as its only member.  I do think that breaking
the code into documented sections is a good plan, but in an effort to
clean up the output, I'm removing this for now.

Change-Id: I3f7e2f704136ebbd1961c5946bac4c2edbd6a371
Signed-off-by: Martin Roth <martin.roth@se-eng.com>
Reviewed-on: http://review.coreboot.org/8070
Tested-by: build bot (Jenkins)
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

src/northbridge/via/vx900/chrome9hd.c

@@ -136,7 +136,7 @@ u32 chrome9hd_fb_size(void)
 }
 
 /**
- * @defgroup vx900_int15
+ * vx900_int15
  *
  * \brief INT15 helpers for Chrome9HD IGP
  *