isci: Adding support for phy enable and disable

Adding support for PHY_FUNC_LINK_RESET and PHY_FUNC_DISABLE. This allow the
sysfs knob enable (both 0 and 1) and link_reset to work properly.

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