hwmon: vexpress: Use devm helper for hwmon device registration

Use devm_hwmon_device_register_with_groups instead of
the old-style manual attributes and hwmon device registration.

Also, unroll the attribute group macros for better code
readability.

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