powerpc/t2080qds: enable eSDHC peripheral clock support

Enable eSDHC peripheral clock support. u-boot and linux will
use SD clock generated by peripheral clock instead of platform
clock.

Signed-off-by: Yangbo Lu <yangbo.lu@freescale.com>
Cc: York Sun <yorksun@freescale.com>
Cc: Pantelis Antoniou <panto@antoniou-consulting.com>
Reviewed-by: York Sun <yorksun@freescale.com>