msm_mpdecision: further simplifications

- redo and simplify enable/disable. move sysfs enabled parameter to
  /sys/module/msm_mpdecision/parameters/enabled consistent
  with other modules. simplify related sysfs functions
- use nr_cpu_ids instead of CONFIG_NR_CPUS. remove redundant if checks
  of nr_cpu_ids from msm_mpdec_work_thread
- redo pause check in msm_mpdec_work_thread
- remove suspend var from msm_mpdec_cpudata, also remove suspend check
  from msm_mpdec_work_thread
- redo and simplify suspend and resume functions
- remove redundant clk_get_rate function, directly call acpuclk_get_rate
- merge mp_decision function with msm_mpdec_work_thread and simplify
  the work thread
- remove startdelay sysfs parameter. there is no point of having it since
  it resets at every boot and used only once after boot
- properly use startdelay only once in the init function instead of an
  if statement repeatedly executed in the work function
- remove redundant exit function