msm: pil: Separate load_image() from device model

Now that the subsystem framework is part of the device model we
can remove the bus layer from PIL. As a first step, separate the
load_image() functionality from the PIL bus. This allows us to
move individual PIL drivers over to loading images directly
without having to call msm_pil_register() first. Instead they
call pil_boot() to boot a processor and pil_shutdown() to
shutdown a processor.

While we're here update the printks by implementing wrappers
around dev_*() that automatically print the descriptor name.

Change-Id: Ica0a866d1a9ca31e3a856da08145dddb6c6b77d0
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>