ARM: milbeaut: fix build with !CONFIG_HOTPLUG_CPU

ARM: milbeaut: fix build with !CONFIG_HOTPLUG_CPU

When HOTPLUG_CPU is disabled, some fields in the smp operations
are not available or needed:

arch/arm/mach-milbeaut/platsmp.c:90:3: error: field designator 'cpu_die' does not refer to any field in type
      'struct smp_operations'
        .cpu_die                = m10v_cpu_die,
         ^
arch/arm/mach-milbeaut/platsmp.c:91:3: error: field designator 'cpu_kill' does not refer to any field in type
      'struct smp_operations'
        .cpu_kill               = m10v_cpu_kill,
         ^

Hide them in an #ifdef like the other platforms do.

Fixes: 9fb29c734f9e ("ARM: milbeaut: Add basic support for Milbeaut m10v SoC")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Olof Johansson <olof@lixom.net>