cpufreq: qcom-hw: enable boost support

At least on sdm850, the 2956800 khz is detected as a boost frequency in
function qcom_cpufreq_hw_read_lut().  Let's enable boost support by
calling cpufreq_enable_boost_support(), so that we can get the boost
frequency by switching it on via 'boost' sysfs entry like below.

 $ echo 1 > /sys/devices/system/cpu/cpufreq/boost

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Tested-by: Steev Klimaszewski <steev@kali.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>