MIPS: AR7: Implement clock API

This patch makes the ar7 clock code implement the Linux clk API. Drivers
using the various clocks available in the SoC are updated accordingly.

Signed-off-by: Florian Fainelli <florian@openwrt.org>
Acked-by: Wim Van Sebroeck <wim@iguana.be>
To: linux-mips@linux-mips.org
Cc: Wim Van Sebroeck <wim@iguana.be>
Cc: netdev@vger.kernel.org
Cc: David Miller <davem@davemloft.net>
Patchwork: http://patchwork.linux-mips.org/patch/881/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>