powerpc/mpc85xx: drop eSDHC periperhal clock code

The below patch added eSDHC periperhal clock code initially.
2d9ca2c7 mmc: fsl_esdhc: Add peripheral clock support

The purpose was to fix up device tree properties "peripheral-frequency"
so that linux could get the periperhal clock by it.
However the implementation on both u-boot and linux was only
for a Freescale SDK release. The linux part implementation had never
been upstreamed. These code should not have been exist on u-boot
mainline.

Let's remove the powerpc part changes but keep the changes in
fsl_esdhc driver. The changes in fsl_esdhc driver could be utilized
to support SD UHS and eMMC HS200/HS400 speed modes for current
Layerscape ARM platforms.

Signed-off-by: Yangbo Lu <yangbo.lu@nxp.com>