arm64: dts: hikey960: Clean up MMC properties and move to proper file

Certain properties should be moved to the board file to reflect
the specific properties of the board, and not the SoC. Move these
properties to proper location and organize properties in both files.

Signed-off-by: Ryan Grachek <ryan@edited.us>
Signed-off-by: Wei Xu <xuwei5@hisilicon.com>