intel_scu_ipc: tidy up unused bits

Delete unused constants IPC_CMD_INDIRECT_RD and IPC_CMD_INDIRECT_WR
Remove multiple inclusion of header file "asm/mrst.h"

Signed-off-by: Sreedhara DS <sreedhara.ds@intel.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Matthew Garrett <mjg@redhat.com>