Instead of open coding DEVICE_ATTR(), use the
DEVICE_ATTR_RW(), DEVICE_ATTR_RO() and DEVICE_ATTR_WO()
macros wherever possible.

This required a few functions to be renamed but the
functionality itself is unchanged.
Signed-off-by: Dwaipayan Ray <dwaipayanray1@gmail.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>