Support --no-smp and --no-acpi for NetBSD.
* include/grub/i386/bsd.h (NETBSD_AB_NOSMP): New definition.
(NETBSD_AB_NOACPI): Likewise.
* loader/i386/bsd.c (netbsd_opts): New entries no-smp and no-acpi.
(netbsd_flags): Add NETBSD_AB_NOSMP, NETBSD_AB_NOACPI.