thermal: hwmon: move hwmon support to single file

In order to improve code organization, this patch
moves the hwmon sysfs support to a file named
thermal_hwmon. This helps to add extra support
for hwmon without scrambling the code.

In order to do this move, the hwmon list head is now
using its own locking. Before, the list used
the global thermal locking. Also, some minor changes
in the code were required, as recommended by checkpatch.pl.

Cc: Zhang Rui <rui.zhang@intel.com>
Cc: linux-pm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Acked-by: Durgadoss R <durgadoss.r@intel.com>
Signed-off-by: Eduardo Valentin <eduardo.valentin@ti.com>