x86: use CONFIG_SYS_COREBOOT to descend into coreboot/ directory

The references of CONFIG_SYS_COREBOOT in arch/x86/cpu/coreboot/Makefile
are redundant because the build system descends into the directory
only when CONFIG_SYS_COREBOOT is defined.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Simon Glass <sjg@chromium.org>
Acked-by: Simon Glass <sjg@chromium.org>

arch/x86/cpu/Makefile

@@ -12,4 +12,4 @@ extra-y	= start.o
 obj-$(CONFIG_X86_RESET_VECTOR) += resetvec.o start16.o
 obj-y	+= interrupts.o cpu.o call64.o
 
-obj-y += $(if $(SOC),$(SOC)/)
+obj-$(CONFIG_SYS_COREBOOT) += coreboot/

arch/x86/cpu/coreboot/Makefile

@@ -13,10 +13,10 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
-obj-$(CONFIG_SYS_COREBOOT) += car.o
-obj-$(CONFIG_SYS_COREBOOT) += coreboot.o
-obj-$(CONFIG_SYS_COREBOOT) += tables.o
-obj-$(CONFIG_SYS_COREBOOT) += ipchecksum.o
-obj-$(CONFIG_SYS_COREBOOT) += sdram.o
-obj-$(CONFIG_SYS_COREBOOT) += timestamp.o
+obj-y += car.o
+obj-y += coreboot.o
+obj-y += tables.o
+obj-y += ipchecksum.o
+obj-y += sdram.o
+obj-y += timestamp.o
 obj-$(CONFIG_PCI) += pci.o