x86: coreboot: Use vendor in the Kconfig

Use VENDOR_COREBOOT instead of TARGET_COREBOOT so we can have multiple
coreboot boards, sharing options. Only SYS_CONFIG_NAME needs to be
defined TARGET_COREBOOT.
Signed-off-by: NSimon Glass <sjg@chromium.org>
Reviewed-by: NBin Meng <bmeng.cn@gmail.com>

arch/x86/cpu/coreboot/Kconfig

-if TARGET_COREBOOT
+if VENDOR_COREBOOT
 
 config SYS_COREBOOT
 	bool

board/coreboot/coreboot/Kconfig

-if TARGET_COREBOOT
+if VENDOR_COREBOOT
 
 config SYS_BOARD
 	default "coreboot"
@@ -9,9 +9,6 @@ config SYS_VENDOR
 config SYS_SOC
 	default "coreboot"
 
-config SYS_CONFIG_NAME
-	default "coreboot"
-
 config SYS_TEXT_BASE
 	default 0x01110000
 
@@ -31,4 +28,11 @@ config SYS_CAR_SIZE
 	help
 	  This option specifies the board specific Cache-As-RAM (CAR) size.
 
+endif  # CONFIG_VENDOR_COREBOOT
+
+if TARGET_COREBOOT
+
+config SYS_CONFIG_NAME
+	default "coreboot"
+
 endif