dt-bindings: hwmon: ltc2978: add support for LT717x

Add LTC7170 and LT7171 to supported devices of LTC2978. It has similar
set of registers to LTC3887, differing only in number of channels and
some PMBUS status and functionalities.

Co-developed-by: Cherrence Sarip <[e-mail]>
Signed-off-by: Cherrence Sarip <[e-mail]>
Signed-off-by: Kim Seer Paller <[e-mail]>
Reviewed-by: Krzysztof Kozlowski <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Guenter Roeck <[e-mail]>

Documentation/devicetree/bindings/hwmon/lltc,ltc2978.yaml

···
 properties:
   compatible:
     enum:
+      - lltc,lt7170
+      - lltc,lt7171
       - lltc,ltc2972
       - lltc,ltc2974
       - lltc,ltc2975
···
     description: |
       list of regulators provided by this controller.
       Valid names of regulators depend on number of supplies supported per device:
+      * lt7170, lt7171 : vout0
       * ltc2972 vout0 - vout1
       * ltc2974, ltc2975 : vout0 - vout3
       * ltc2977, ltc2979, ltc2980, ltm2987 : vout0 - vout7