msm: pil: Reorg registration API

Instead of having pil device driver authors register struct
pil_device pointers, have them register a set of ops along with
the important parts of struct pil_device. This allows us to
separate the platform_device from the pil_device so that future
device driver authors can move away from the platform bus. Plus,
this allows us to hide the details of struct pil_device outside
of peripheral-loader.c.

Change-Id: I0945c0bc2447207270efcd3fb935437c449edc63
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>