docs: hwmon: add emc2305.rst to docs

Add description of emc2305 driver.

Signed-off-by: Michael Shych <michaelsh@nvidia.com>
Reviewed-by: Vadim Pasternak <vadimp@nvidia.com>
Link: https://lore.kernel.org/r/20220810171552.56417-4-michaelsh@nvidia.com


[groeck: Fixed htmldocs warnings]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>