docs: hwmon: Update documentation for isl68137 pmbus driver

Update documentation to include reference information for newly
supported 2nd generation Renesas digital multiphase voltage regulators.
Also update branding from Intersil to Renesas.

Signed-off-by: Grant Peltier <[email protected]>
Link: https://lore.kernel.org/r/1588e5e89d6a9623464036cf8fbdb9b18785894b.1584720563.git.grantpeltier93@gmail.com
Signed-off-by: Guenter Roeck <[email protected]>

Author: gfpeltier