Currently we see the following error when using the SAI audio
driver on mx7:

Division by zero in kernel.
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.8.0-rc3-next-20160823
Hardware name: Freescale i.MX7 Dual (Device Tree)
Backtrace:
[<c010b70c>] (dump_backtrace) from [<c010b8a8>] (show_stack+0x18)
r6:60000013 r5:ffffffff r4:00000000 r3:00000000
[<c010b890>] (show_stack) from [<c03e9324>] (dump_stack+0xb0/0xe)
[<c03e9274>] (dump_stack) from [<c010b578>] (__div0+0x18/0x20)
r8:00000000 r7:ffffffff r6:ffffffff r5:00000000 r4:00000000 r3:0
[<c010b560>] (__div0) from [<c03e795c>] (Ldiv0_64+0x8/0x18)
[<c06cd860>] (divider_get_val) from [<c06cda28>] (clk_divider_se)

This error happens due to the lack of definition of the
IMX7D_PLL_AUDIO_TEST_DIV/IMX7D_PLL_AUDIO_POST_DIV clocks.

Add support for them.

Tested on a imx7s-warp board.
Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>