devfreq: governor_cpubw_hwmon: Remove sample_ms and fix round up of freq

devfreq already provides a sysfs interface for changing polling/sampling
period. So, there is no need for the governor to separately expose
sampling_ms. Also, sampling_ms had to be explicitly updated whenever
polling_ms was updated for the governor to function correctly. Make the
interface simpler by combining sample_ms with polling_interval control
provided by devfreq.

The rounding of freq to multiples of bw_step is unnecessary since the
devfreq device already does the rounding to the next valid level. Rounding
of AB to multiples of bw_step is still necessary since it's a vote that's
summed up and doesn't have a direct 1-to-1 mapping to frequencies.

Also update default bw_step to 190 MB/s instead of 200 MB/s to account for
the fact that MB/s to MHz conversion needs to take into account the
difference in the meaning of M (2^20 vs 10^6) between MB and MHz. Similarly
also update io_percent to 16.

Change-Id: I5fea989c647955103de3813be8eb9ec612f131bc
Signed-off-by: Saravana Kannan <skannan@codeaurora.org>