mmc: fsl_esdhc: actually enable cache snooping on mpc830x

The reference manuals for MPC8308 and MPC8309 both say that the
esdhcctl aka DMA Control Register "is implemented as SDHCCR" in the
System configuration registers. Unfortunately, that doesn't mean that
the registers are just mirrors of each other - any write to esdhcctl
is simply ignored. So to actually enable cache snooping, we
unfortunately have to add a little ifdeffery.

There is, naturally, no description of the bit fields of esdhcctl in
the MPC8309 manual, but comparing the description of esdhcctl from the
LS1021A reference manual to the description of the sdhccr in MPC8309,
one also finds that the fields are bit-reversed, so the bit to set is
0x02000000 rather than 0x00000040 - this is also what board_mmc_init()
uses in the two gdsys/mpc8308/ boards.

Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Reviewed-by: Yangbo Lu <yangbo.lu@nxp.com>