s390: use generic vga.h header file

The generic vga.h contains a couple of defines, which do no harm on
s390. Therefore use the generic version and git rid of the s390
specific empty header file.
Suggested-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

arch/s390/include/asm/vga.h

-/* SPDX-License-Identifier: GPL-2.0 */
-#ifndef _ASM_S390_VGA_H
-#define _ASM_S390_VGA_H
-
-/* Avoid compile errors due to missing asm/vga.h */
-
-#endif /* _ASM_S390_VGA_H */