soc: qcom: msm_performance: Include msm-core header

msm-core module is no more needed with energy aware scheduler.

Update msm-core header with symbols exported and include it
in msm_performance module to avoid undefined references to
get_cpu_pwr_stats when msm-core is disabled.

Change-Id: Ib25715b5401f8d91f5dba6cdb2d0c2d3d81e3329
Signed-off-by: Maulik Shah <mkshah@codeaurora.org>