vboot: Move remaining features out of vendorcode/google/chromeos

This patch attempts to finish the separation between CONFIG_VBOOT and
CONFIG_CHROMEOS by moving the remaining options and code (including
image generation code for things like FWID and GBB flags, which are
intrinsic to vboot itself) from src/vendorcode/google/chromeos to
src/vboot. Also taking this opportunity to namespace all VBOOT Kconfig
options, and clean up menuconfig visibility for them (i.e. some options
were visible even though they were tied to the hardware while others
were invisible even though it might make sense to change them).

CQ-DEPEND=CL:459088

Change-Id: I3e2e31150ebf5a96b6fe507ebeb53a41ecf88122
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://review.coreboot.org/18984
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/arch/x86/bootblock_simple.c

@@ -28,7 +28,7 @@ static void main(unsigned long bist)
 #endif
 	}
 
-#if CONFIG_SEPARATE_VERSTAGE
+#if CONFIG_VBOOT_SEPARATE_VERSTAGE
 	const char *target1 = "fallback/verstage";
 #else
 	const char *target1 = "fallback/romstage";