misc: qpnp: add snapshot of qpnp-misc documentation

qpnp-misc driver supports accessing MISC peripheral registers
in certain PMICs.

This is snapshot of the qpnp-misc device documentation as of msm-4.9
'commit 98cddae6cdce ("Merge "msm: camera: Fix media_entity
assignment")'.

Change-Id: Ic1e820e98dceb66195c56785e50590f1ba92f830
Signed-off-by: Tirupathi Reddy <tirupath@codeaurora.org>