dt-bindings: hwmon: Add Baikal-T1 PVT sensor binding

dt-bindings: hwmon: Add Baikal-T1 PVT sensor binding

Baikal-T1 SoC is equipped with an embedded process, voltage and
temperature sensor to monitor the chip internal environment like
temperature, supply voltage and transistors performance.

This bindings describes the external Baikal-T1 PVT control interfaces
like MMIO registers space, interrupt request number and clocks source.
These are then used by the corresponding hwmon device driver to
implement the sysfs files-based access to the sensors functionality.

Co-developed-by: Maxim Kaurkin <maxim.kaurkin@baikalelectronics.ru>
Signed-off-by: Maxim Kaurkin <maxim.kaurkin@baikalelectronics.ru>
Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Reviewed-by: Rob Herring <robh@kernel.org>
Cc: Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: linux-mips@vger.kernel.org
Signed-off-by: Guenter Roeck <linux@roeck-us.net>