MIPS: alchemy: Convert to clk_hw based provider APIs

We're removing struct clk from the clk provider API, so switch
this code to using the clk_hw based provider APIs.

Cc: Manuel Lauss <manuel.lauss@gmail.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Linux-MIPS <linux-mips@linux-mips.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>