x86/IRQ: flip legacy and dynamic vector ranges

x86/IRQ: flip legacy and dynamic vector ranges

There's no reason to have the PIC vectors (which are typically entirely
unused on 64-bit systems anyway) right below the high priority ones. Put
them in the lowest possible range, and shift the dynamic vector range up
accordingly. This is to reduce the priority of PIC vectors in the LAPIC
vs all other ones.

Note that irq_move_cleanup_interrupt(), despite using
FIRST_DYNAMIC_VECTOR, does not get touched, as PIC interrupts aren't
movable.

Suggested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>