loader: implement framebuffer console

Draw console on efi.
Add vbe framebuffer for BIOS loader (vbe off, vbe on, vbe list,
vbe set xxx).
autoload font (/boot/fonts) based on resolution and font size.
Add command loadfont (set font by file) and
variable screen.font (set font by size). Pass loaded font to kernel.

Export variables:
screen.height
screen.width
screen.depth

Add gfx primitives to draw the screen and put png image on the screen.
Rework menu draw to iterate list of consoles to enamble device specific
output.

Probably something else I forgot...

Relnotes: yes
Differential Revision: https://reviews.freebsd.org/D27420

stand/Makefile

@@ -25,6 +25,8 @@ S.${MK_FORTH}+=		forth
 S.${MK_LOADER_LUA}+=	liblua
 S.${MK_LOADER_LUA}+=	lua
 S.yes+=			defaults
+S.yes+=			fonts
+S.yes+=			images
 S.yes+=			man
 
 .if ${MK_FORTH} != "no"

stand/common/bootstrap.h

@@ -32,6 +32,7 @@
 #include <sys/types.h>
 #include <sys/queue.h>
 #include <sys/linker_set.h>
+#include <stdbool.h>
 
 #include "readin.h"
 
@@ -119,6 +120,8 @@ struct console
 };
 extern struct console *consoles[];
 void cons_probe(void);
+bool		cons_update_mode(bool);
+void		autoload_font(bool);
 
 /*
  * Plug-and-play enumerator/configurator interface.
@@ -258,6 +261,8 @@ int file_addmodule(struct preloaded_file *, char *, int,
     struct kernel_module **);
 void file_removemetadata(struct preloaded_file *fp);
 
+vm_offset_t build_font_module(vm_offset_t);
+
 /* MI module loaders */
 #ifdef __elfN
 /* Relocation types. */