x86/power: Fix kernel-doc warnings in cpu.c

Fixes the following kernel-doc warnings:

 arch/x86/power/cpu.c:76: warning: Function parameter or
  member 'ctxt' not described in '__save_processor_state'
 arch/x86/power/cpu.c:192: warning: Function parameter or
  member 'ctxt' not described in '__restore_processor_state'

Signed-off-by: Baokun Li <libaokun1@huawei.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210618022421.1595596-1-libaokun1@huawei.com