cpufreq: Use pr_info() for driver registration and unregistration

Many subsystems depend on cpufreq API for CPU frequency scaling.
Cpufreq API is expected to fail until cpufreq device registers.

Change pr_debug() to pr_info() so that user could determine when
cpufreq API becomes available during boot from kernel messages. This
is crucial to understand whether a cpufreq API failure is benign
during early boot.

Change-Id: Id2dfa009ae33859ec3efcdb29a3296e891852c6a
Signed-off-by: Junjie Wu <junjiew@codeaurora.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Rohit Gupta <rohgup@codeaurora.org>
Signed-off-by: Jonathan Avila <avilaj@codeaurora.org>