console/font: Refactor font support code selection logic

The current Makefile rules to build font support are messy and buggy.
Replace them by Kconfig rules:
  - Introduce CONFIG_FONT_SUPPORT, which controls the building of all font
    code,
  - Select CONFIG_FONT_SUPPORT for all drivers that use fonts,
  - Select CONFIG_FONT_8x16 for all drivers that default to the VGA8x16
    font,
  - Drop the bogus console dependency for CONFIG_VIDEO_VIVI,
  - Always process drivers/video/console/Makefile, as some drivers need
    fonts even if CONFIG_VT is not set.

This fixes (if CONFIG_SOLO6X10=y and there are no built-in console
drivers):

drivers/built-in.o: In function `solo_osd_print':
drivers/staging/media/solo6x10/solo6x10-enc.c:144: undefined reference to `.find_font'

This fixes (if CONFIG_VT=n):

drivers/built-in.o: In function `vivi_init':
vivi.c:(.init.text+0x1a3da): undefined reference to `find_font'

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com> [original part]
Acked-by: Randy Dunlap <rdunlap@infradead.org> [drivers/video/Makefile]
diff --git a/drivers/video/console/Makefile b/drivers/video/console/Makefile
index a862e91..3a11b63 100644
--- a/drivers/video/console/Makefile
+++ b/drivers/video/console/Makefile
@@ -18,14 +18,14 @@
 
 font-objs += $(font-objs-y)
 
-# Each configuration option enables a list of files.
+obj-$(CONFIG_FONT_SUPPORT)         += font.o
 
 obj-$(CONFIG_DUMMY_CONSOLE)       += dummycon.o
-obj-$(CONFIG_SGI_NEWPORT_CONSOLE) += newport_con.o font.o
-obj-$(CONFIG_STI_CONSOLE)         += sticon.o sticore.o font.o
+obj-$(CONFIG_SGI_NEWPORT_CONSOLE) += newport_con.o
+obj-$(CONFIG_STI_CONSOLE)         += sticon.o sticore.o
 obj-$(CONFIG_VGA_CONSOLE)         += vgacon.o
 obj-$(CONFIG_MDA_CONSOLE)         += mdacon.o
-obj-$(CONFIG_FRAMEBUFFER_CONSOLE) += fbcon.o bitblit.o font.o softcursor.o
+obj-$(CONFIG_FRAMEBUFFER_CONSOLE) += fbcon.o bitblit.o softcursor.o
 ifeq ($(CONFIG_FB_TILEBLITTING),y)
 obj-$(CONFIG_FRAMEBUFFER_CONSOLE)     += tileblit.o
 endif
@@ -34,8 +34,4 @@
                                          fbcon_ccw.o
 endif
 
-obj-$(CONFIG_FB_STI)              += sticore.o font.o
-
-ifeq ($(CONFIG_USB_SISUSBVGA_CON),y)
-obj-$(CONFIG_USB_SISUSBVGA)           += font.o
-endif
+obj-$(CONFIG_FB_STI)              += sticore.o