hwmon: (fam15h_power) Add ratio of Tsample to the PTSC period

This patch adds a member (cpu_pwr_sample_ratio) of fam15h_power_data,
that represents the ratio of compute unit power accumulator sample
period to the PTSC counter period.

Tsample: compute unit power accumulator sample period
Tref: the performance timestamp counter period
PTSC: performance timestamp counter

Signed-off-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>