usbdebug: Fix boards without EARLY_CBMEM_INIT

The main usbdebug file lib/usbdebug.c was removed from romstage
build with commit f8bf5a10 but the chipset-specific parts were not,
leading to unresolved symbol errors for AMD platforms.

Add a silent Kconfig variable USBDEBUG_IN_ROMSTAGE for convenient
use of this feature.

Change-Id: I0cd3fccf2612cf08497aa5c3750c89bf43ff69be
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/3983
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@google.com>

src/lib/Makefile.inc

@@ -49,11 +49,11 @@ romstage-$(CONFIG_CONSOLE_SERIAL8250) += uart8250.c
 romstage-$(CONFIG_CONSOLE_SERIAL8250MEM) += uart8250mem.c
 romstage-$(CONFIG_CONSOLE_NE2K) += ne2k.c
 romstage-$(CONFIG_SPKMODEM) += spkmodem.c
+romstage-$(CONFIG_USBDEBUG_IN_ROMSTAGE) += usbdebug.c
 
 ifeq ($(CONFIG_EARLY_CBMEM_INIT),y)
 romstage-$(CONFIG_COLLECT_TIMESTAMPS) += timestamp.c
 romstage-$(CONFIG_CONSOLE_CBMEM) += cbmem_console.c
-romstage-$(CONFIG_USBDEBUG) += usbdebug.c
 endif
 
 romstage-y += compute_ip_checksum.c

src/lib/usbdebug.c

@@ -581,7 +581,7 @@ err:
 
 static void enable_usbdebug(void)
 {
-#if defined(__PRE_RAM__) || !(CONFIG_EARLY_CONSOLE && CONFIG_EARLY_CBMEM_INIT)
+#if defined(__PRE_RAM__) || !CONFIG_USBDEBUG_IN_ROMSTAGE
 	pci_devfn_t dbg_dev = pci_ehci_dbg_dev(CONFIG_USBDEBUG_HCD_INDEX);
 	pci_ehci_dbg_enable(dbg_dev, CONFIG_EHCI_BAR);
 #endif