x86: Use section .data.page_aligned for the idt_table.

The .data.idt section is just squashed into the .data.page_aligned
output section by the linker script anyway, so it might as well be in
the .data.page_aligned section.

This eliminates all references to .data.idt on x86.

Signed-off-by: Tim Abbott <tabbott@ksplice.com>
Cc: Ingo Molnar <mingo@redhat.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>