cpufreq: qcom: pass pvs_name size along with its buffer

The get_version handler takes a pvs_name buffer and can override it with
the speed, pvs, and pvs version values. The function does not take as
argument the buffer size and is currently being determined by calling
`sizeof("speedXX-pvsXX-vXX")`. This is not great because it duplicates
the string in several locations which makes it error-prone if we need to
modify the string someday. Also since the buffer and its size are tied
together, it makes sense that they should both be passed together to the
get_version as parameters.

This commit makes sure that the PVS name template string is only
defined once, and that the pvs_name buffer is passed with its size.

Signed-off-by: Fabien Parent <fabien.parent@linaro.org>