x86: Add an option to control the position of U-Boot

The existing work-around for positioning U-Boot in the ROM when it
actually runs from RAM still exists and there is not obvious way to change
this.

Add a proper Kconfig option to handle this case. This also adds a new bool
property to indicate whether CONFIG_SYS_TEXT_BASE exists.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 64f1673..9d7ff3c 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -899,4 +899,9 @@
 	depends on INTEL_CAR_CQOS
 	default 0x20000 # 128 KB
 
+config X86_OFFSET_U_BOOT
+	hex "Offset of U-Boot in ROM image"
+	depends on HAVE_SYS_TEXT_BASE
+	default SYS_TEXT_BASE
+
 endmenu