msm: ipc_logging: remove internal details from header

Some internal details no longer need to be shared between modules, so
they can be moved to the main implementation file to avoid unnecessary
coupling in the future.

Change-Id: Ie8774f0c95f5ec6a56a95c57fea79032194eb05e
Signed-off-by: Eric Holmberg <eholmber@codeaurora.org>