soc: qcom: icc-bwmon: store count unit per variant

Versions v4 and v5 of BWMON on SDM845 use different unit count, so allow
easier variant customization by storing its value in struct
icc_bwmon_data.

Cc: Rajendra Nayak <quic_rjendra@quicinc.com>
Cc: Sibi Sankar <quic_sibis@quicinc.com>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Sibi Sankar <quic_sibis@quicinc.com>
Tested-by: Steev Klimaszewski <steev@kali.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20220728113748.170548-7-krzysztof.kozlowski@linaro.org