ppc/85xx: Use CONFIG_FSL_ESDHC to enable sdhc clk

Enable eSDHC Clock based on generic CONFIG_FSL_ESDHC define instead of a
platform define.  This will enable all the 85xx platforms to use sdhc_clk
based on CONFIG_FSL_ESDHC.

Signed-off-by: Gao Guanhua <B22826@freescale.com>
Signed-off-by: Dipen Dudhat <dipen.dudhat@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>