clk: npcm7xx: add 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>
[sboyd@kernel.org: Drop clk_get()s, cleanup whitespace, drop unused
includes, fix static checker warnings]
Signed-off-by: Stephen Boyd <sboyd@kernel.org>