loader: BIOS loader should not build framebuffer support by default

[tsoome]

Summary

Since BIOS loader size is limited, we need to be careful with
including features. Lets keep framebuffer version with optional build.

To enable, one would need to add BOOT_FRAMEBUFFER_MODE=yes in src.conf.

[imp]

So I think this is a great next step.
I'd love gfx to be 100% optional, but there's still some interdependencies with lua and 4th that make that much harder than it needs to be.
It might also be better to move the framebuffer stuff more into vbe.c since that might allow fewer ifdefs, but I've not delved enough to know if that's really a good idea.

stand/common/gfx_fb.c

1446

Why not define FRAMEBUFFER_MODE for EFI too? Then it could be an option there. at $WORK we've had some systems get cranky with the graphics, though they all were early pre-release NDA systems that the late pre-release version fixed. Since we do serial + video, this code is bypassed anyway on our production systems and there's been a push at work to reduce our attack surface where ever possible by not even compiling in code we know we won't execute.

stand/common/gfx_fb_stub.c

109

It would be great if this file were no longer required at all.
None of this makes any sense for my kboot program.

stand/i386/libi386/vidconsole.c

899

I'd be tempted to eliminate this variable entirely in !framebuffer_mode...
But this is fine.