dt-bindings: phy: phy-cadence-sierra: Add binding to model Sierra as clock provider

Add #clock-cells binding to model Sierra as clock provider and include
clock IDs for PLL_CMNLC and PLL_CMNLC1.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210319124128.13308-12-kishon@ti.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>