msm: remove setup and last remnants of MSM_IMEM_BASE

Now that there are no users of MSM_IMEM_BASE we can remove the setup
code associated and any remaining references to it.

Change-Id: I38d099e448f87af1fd2f140505dde7712f9d28b8
Signed-off-by: Kumar Gala <galak@codeaurora.org>