use acpi.h include instead of manually adding acpi_slp_type.

use acpi.h include instead of manually adding acpi_slp_type.

Change-Id: I2a3aaf10e453fa6cce8a993356f2a0587178209a
Signed-off-by: Stefan Reinauer <reinauer@google.com>
Reviewed-on: http://review.coreboot.org/276
Tested-by: build bot (Jenkins)
Reviewed-by: Uwe Hermann <uwe@hermann-uwe.de>