msm: cpufreq: Remove use of cpu_is_* API

cpu_is_* API is deprecated. Relevant targets now rely on is_sync for
proper cpufreq mask setup. Remove unnecessary cpu_is_* calls from
cpufreq.c

Change-Id: I326d24c24f37b34fba36dbf9fc08aa5071180b51
Signed-off-by: Junjie Wu <junjiew@codeaurora.org>