msm_mpdecision: various fixes and tweaks

- fix get_slowest_cpu_rate(): don't cut off rate to int
- fix get_slowest_cpu_rate(): don't use values from an offline cpu
- fix get_slowest_cpu(): don't return cpu0.
- tweak hotplug thresholds

Signed-off-by: Dennis Rassmann <showp1984@gmail.com>