dt-binding: clk: npcm750: Add binding for Nuvoton NPCM7XX Clock

* Nuvoton NPCM7XX Clock Controller

Nuvoton Poleg BMC NPCM7XX contains an integrated clock controller, which
generates and supplies clocks to all modules within the BMC.

Signed-off-by: Tali Perry <tali.perry1@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>