x86/KASLR: Update KERNEL_IMAGE_SIZE description

Currently CONFIG_RANDOMIZE_BASE=y is set by default, which makes some of the
old comments above the KERNEL_IMAGE_SIZE definition out of date. Update them
to the current state of affairs.

Signed-off-by: Baoquan He <bhe@redhat.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: corbet@lwn.net
Cc: linux-doc@vger.kernel.org
Cc: thgarnie@google.com
Link: http://lkml.kernel.org/r/20181006084327.27467-2-bhe@redhat.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>