x86: Support ROMs on other archs

We shouldn't assume that the VGA ROM can always be loaded at c0000. This
is only true on x86 machines.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/arch/x86/include/asm/u-boot-x86.h b/arch/x86/include/asm/u-boot-x86.h
index 36145cb..b98afa8 100644
--- a/arch/x86/include/asm/u-boot-x86.h
+++ b/arch/x86/include/asm/u-boot-x86.h
@@ -70,4 +70,6 @@
 
 void quick_ram_check(void);
 
+#define PCI_VGA_RAM_IMAGE_START		0xc0000
+
 #endif	/* _U_BOOT_I386_H_ */