vboot: Separate board name and version number in FWID with a dot

It's standard practice in vboot that the FWID consists of
<board_name>.<version_number> (e.g. Google_Kevin.8785.57.0). In fact,
some tools rely on this and cut the string at the first dot to
separate the two.

The current Kconfig default in coreboot instead leads to ugly,
parser-breaking FWIDs like Google_Kevin4.5-1234-5678abcd. This patch
fixes that.

Change-Id: I65cd5285c69e2e485d55a41a65d735f6a2291c16
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://review.coreboot.org/19487
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

src/vboot/Kconfig

@@ -206,7 +206,7 @@ config VBOOT_FWID_MODEL
 
 config VBOOT_FWID_VERSION
 	string "Firmware ID version"
-	default "$(KERNELVERSION)"
+	default ".$(KERNELVERSION)"
 	help
 	  This is the second part of the FWID written to various regions of a
 	  vboot firmware image to identify its version.