[x86] remove uses of magic macros for boot_params access

Instead of using magic macros for boot_params access, simply use the
boot_params structure.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index f01bfcd..493a083 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1137,9 +1137,10 @@
 	new_cpu_data.x86_capability[0] = cpuid_edx(1);
 
 	/* Poke various useful things into boot_params */
-	LOADER_TYPE = (9 << 4) | 0;
-	INITRD_START = xen_start_info->mod_start ? __pa(xen_start_info->mod_start) : 0;
-	INITRD_SIZE = xen_start_info->mod_len;
+	boot_params.hdr.type_of_loader = (9 << 4) | 0;
+	boot_params.hdr.ramdisk_image = xen_start_info->mod_start
+		? __pa(xen_start_info->mod_start) : 0;
+	boot_params.hdr.ramdisk_size = xen_start_info->mod_len;
 
 	/* Start the world */
 	start_kernel();