x86: coreboot: Drop USB init on startup

This is very annoying as it is quite slow on many machines. Also, U-Boot
has an existing 'preboot' mechanism to enable this feature if desired.

Drop this code so that it is possible to choose whether to init USB or
not.

Use the existing USE_PREBOOT mechanism instead.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

arch/x86/cpu/coreboot/Kconfig

@@ -25,6 +25,7 @@ config SYS_COREBOOT
 	imply FS_CBFS
 	imply CBMEM_CONSOLE
 	imply X86_TSC_READ_BASE
+	imply USE_PREBOOT
 	select BINMAN if X86_64
 
 endif

arch/x86/cpu/coreboot/coreboot.c

@@ -86,10 +86,6 @@ static int last_stage_init(void)
 	if (IS_ENABLED(CONFIG_SPL_BUILD))
 		return 0;
 
-	/* start usb so that usb keyboard can be used as input device */
-	if (IS_ENABLED(CONFIG_USB_KEYBOARD))
-		usb_init();
-
 	board_final_init();
 
 	return 0;

doc/board/coreboot/coreboot.rst

@@ -83,6 +83,13 @@ build in `$CBDIR`::
       -device ide-hd,drive=disk,bus=ahci.0 \
 
 
+USB keyboard
+------------
+
+The `CONFIG_USE_PREBOOT` option is enabled by default, meaning that USB starts
+up just before the command-line starts. This allows user interaction on
+non-laptop devices which use a USB keyboard.
+
 CBFS access
 -----------