x86-64: don't set the early IDT to point directly to 'early_idt_handler'

The code requires the use of the proper per-exception-vector stub
functions (set up as the early_idt_handlers[] array - note the 's') that
make sure to set up the error vector number.  This is true regardless of
whether CONFIG_EARLY_PRINTK is set or not.

Why? The stack offset for the comparison of __KERNEL_CS won't be right
otherwise, nor will the new check (from commit 8170e6bed465: "x86,
64bit: Use a #PF handler to materialize early mappings on demand") for
the page fault exception vector.

Acked-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>