Documentation: msm: Snapshot of imem documentation.

This is snapshot of the imem documentation file as of msm-4.14 commit
<dfb894c59eaf234>. (Merge "clk: qcom: gcc: Add new frequencies for
emac_clk_src").

Change-Id: Ie9e5a7e4ee770864178e95a4ab0ce2a03ac73037
Signed-off-by: Rishabh Bhatnagar <rishabhb@codeaurora.org>