dts: fixes in the dts of em_starterkit em9d configuration

* em9d is configured to use ccm, and no sram
* choose dccm as virtual sram to generate the correct definitions
of CONFIG_SRAM_XXX which are used in many places, e.g. lib-hooks.c.

Signed-off-by: Wayne Ren <wei.ren@synopsys.com>