x86/64/defconfig: Add CONFIG_IRQ_REMAP

x2apic is enabled in the defconfig, and interrupt remapping is an
architectural dependency of x2apic as per the Intel SDM:

  Routing of device interrupts to local APIC units operating in x2APIC
  mode requires use of the interrupt-remapping architecture specified in
  the Intel® Virtualization Technology for Directed I/O (Revision 1.3
  and/or later versions).

Enable CONFIG_IRQ_REMAP in defconfig so that a defconfig kernel on bare metal
actually uses x2apic.

Co-developed-by: Rahul Bukte <rahul.bukte@sony.com>
Signed-off-by: Rahul Bukte <rahul.bukte@sony.com>
Signed-off-by: Shashank Balaji <shashank.mahadasyam@sony.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Sohil Mehta <sohil.mehta@intel.com>
Acked-by: Thomas Gleixner <tglx@kernel.org>
Link: https://patch.msgid.link/20260306-x2apic-fix-v2-2-bee99c12efa3@sony.com