imx: mx7: enable CONFIG_FSL_CLK

This commit "677f970b" introduce a new
macro "CONFIG_FSL_CLK" that get_clocks() should not be limited by ESDHC.

But that patch missed to enable it for i.MX7. THis patch enables
CONFIG_FSL_CLK to let get_clocks work.

Signed-off-by: Peng Fan <Peng.Fan@freescale.com>
Cc: Adrian Alonso <aalonso@freescale.com>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Fabio Estevam <fabio.estevam@freescale.com>