omap2plus-cpufreq: set transition latency to 30ms

Vishwanath says 30ms is best, so I'm gonna agree with him:
http://www.mail-archive.com/linaro-dev@lists.linaro.org/msg01373.html
raise nitro_rate from 1200000 to 1350000

Change-Id: Id6c7642f618273937b127e57c0d3e5ec0060c7ee