isci: cleanup remote device construction and comments

The construction routines scic_remote_device_[de]a_construct both reference
the need to call scic_remote_device_construct first.  Delete that comment and
just have them call it explicitly, also:
* move the comments from header to source
* delete dead references to scic_[de]a_remote_device_add_phy

Signed-off-by: Dan Williams <dan.j.williams@intel.com>