x86: switch to .rodata.compressed in arch/x86/boot/compressed/vmlinux_??.scr

vmlinux_64 and vmlinux_32.scr are now identical

size shows an expected movement from .text to .rodata and 4 extra bytes
of padding.

Signed-off-by: Ian Campbell <ijc@hellion.org.uk>
Cc: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>