cris: Wire up asm-generic/vga.h

When compiling several DRM related files:

include/video/vga.h:22:21: fatal error: asm/vga.h: No such file or directory
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

arch/cris/include/asm/Kbuild

@@ -9,4 +9,5 @@ generic-y += kvm_para.h
 generic-y += linkage.h
 generic-y += module.h
 generic-y += trace_clock.h
+generic-y += vga.h
 generic-y += xor.h