mei: make host csr and me csr internal to hw-me

Move csr reading into me hardware functional calls.
Since we gave up on registers caching we remove some of the unnecessary
queries in mei_hw_init ane mei_reset functions.

We add mei_hw_config function to wrap up host buffer depth configuration.

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>