Include xf86Cursor.h instead of xf86RamDac.h

ramdac drivers have been removed from xserver since version 21.0.99.1
and xorg/xserver@f0385fb4 resulting in the following build failure:

In file included from ../../src/cg6_cursor.c:31:
../../src/cg6.h:29:10: fatal error: xf86RamDac.h: No such file or directory
   29 | #include "xf86RamDac.h"
      |          ^~~~~~~~~~~~~~

but xf86RamDac.h in turn included xf86Cursor.h which we still need.

Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>