ACPI / IPMI: Cleanup some Kconfig codes

This (trivial) patch:
1. Deletes duplicate Kconfig dependency as there is "if IPMI_HANDLER"
   around "IPMI_SI".

Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Reviewed-by: Huang Ying <ying.huang@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>