ARM: imx: AHB rate must be set to 132MHz on i.mx6sl

The reset value of AHB divider is 3, so current AHB rate
is 99MHz which is not correct for kernel, need to ensure
AHB rate is 132MHz in clk driver, as ipg is sourcing from
AHB, and it should be 66MHz by default.

Signed-off-by: Anson Huang <b20788@freescale.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>