[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>

arch/x86/boot/Makefile

@@ -39,6 +39,7 @@ setup-y		+= printf.o string.o tty.o video.o version.o voyager.o
 setup-y		+= video-vga.o
 setup-y		+= video-vesa.o
 setup-y		+= video-bios.o
+
 targets		+= $(setup-y)
 hostprogs-y	:= tools/build