arm64: dts: ls1088a: support eMMC HS200 speed mode for RDB board

This patch is to add eMMC HS200 speed mode support on ls1088ardb
whose controller and peripheral circut support such capability.
And clocks dts property is needed for driver to get peripheral
clock value used for this speed mode.

Signed-off-by: Yangbo Lu <yangbo.lu@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>