mpc83xx: 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 83xx
platforms to use sdhc_clk based on CONFIG_FSL_ESDHC.  It's
the same patch as commit 6b9ea08c
for the ppc/85xx.

Signed-off-by: Rini <rini@arvoo.nl>
Signed-off-by: Kim Phillips <kim.phillips@freescale.com>