hwmon: (vexpress) Use legal hwmon device names

The driver used to directly us a DT 'compatible' property for
the 'name' attribute of the hwmon devices. Unfortunately it
contains '-' which is illegal in this context. It messes up
libsensors and thus every application using it.

Fixed by providing equivalent (and simpler) name strings.

Reported-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Pawel Moll <pawel.moll@arm.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>