lib/edid: Split out fill_lb_framebuffer()

Place it into new edid_fill_fb.c, and invert the logic of the Kconfig
guard (NATIVE_VGA_INIT_USE_EDID is now !NO_EDID_FILL_FB). It has to be
selected by all drivers that use MAINBOARD_DO_NATIVE_VGA_INIT but pro-
vide their own fill_lb_framebuffer() implementation.

Change-Id: I90634b835bd8e2d150b1c714328a5b2774d891bd
Signed-off-by: Nico Huber <nico.huber@secunet.com>
Reviewed-on: https://review.coreboot.org/19764
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>

src/Kconfig

@@ -1043,6 +1043,9 @@ endmenu
 ###############################################################################
 # Set variables with no prompt - these can be set anywhere, and putting at
 # the end of this file gives the most flexibility.
+
+source "src/lib/Kconfig"
+
 config ENABLE_APIC_EXT_ID
 	bool
 	default n