x86/idt: Prepare for table based init

The IDT setup code is handled in several places. All of them use variants
of set_intr_gate() inlines. This can be done with a table based
initialization, which allows to reduce the inline zoo and puts all IDT
related code and information into a single place.

Add the infrastructure.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/20170828064958.849877032@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>