x86: Use X86_16BIT_INIT instead of X86_RESET_VECTOR

Use this new option to control the location of 16-bit init. This will allow
us to place this in SPL if needed.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/arch/x86/cpu/Makefile b/arch/x86/cpu/Makefile
index f5b8c9e..fd81310 100644
--- a/arch/x86/cpu/Makefile
+++ b/arch/x86/cpu/Makefile
@@ -9,7 +9,7 @@
 #
 
 extra-y	= start.o
-obj-$(CONFIG_X86_RESET_VECTOR) += resetvec.o start16.o
+extra-$(CONFIG_$(SPL_)X86_16BIT_INIT) += resetvec.o start16.o
 obj-y	+= interrupts.o cpu.o cpu_x86.o call64.o setjmp.o
 
 AFLAGS_REMOVE_call32.o := -mregparm=3 \