linux/vt_buffer.h: allow either builtin or modular for macros

linux/vt_buffer.h: allow either builtin or modular for macros

Fix build errors on ARCH=alpha when CONFIG_MDA_CONSOLE=m.
This allows the ARCH macros to be the only ones defined.

In file included from ../drivers/video/console/mdacon.c:37:
../arch/alpha/include/asm/vga.h:17:40: error: expected identifier or '(' before 'volatile'
   17 | static inline void scr_writew(u16 val, volatile u16 *addr)
      |                                        ^~~~~~~~
../include/linux/vt_buffer.h:24:34: note: in definition of macro 'scr_writew'
   24 | #define scr_writew(val, addr) (*(addr) = (val))
      |                                  ^~~~
../include/linux/vt_buffer.h:24:40: error: expected ')' before '=' token
   24 | #define scr_writew(val, addr) (*(addr) = (val))
      |                                        ^
../arch/alpha/include/asm/vga.h:17:20: note: in expansion of macro 'scr_writew'
   17 | static inline void scr_writew(u16 val, volatile u16 *addr)
      |                    ^~~~~~~~~~
../arch/alpha/include/asm/vga.h:25:29: error: expected identifier or '(' before 'volatile'
   25 | static inline u16 scr_readw(volatile const u16 *addr)
      |                             ^~~~~~~~

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jirislaby@kernel.org>
Cc: dri-devel@lists.freedesktop.org
Cc: linux-fbdev@vger.kernel.org
Link: https://lore.kernel.org/r/20230329021529.16188-1-rdunlap@infradead.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>