driver/fsp2_0: Include stdint header file in api.h

'bool' type is reported undefined due to missing stdint.h inclusion,
Fix it by including the same.

Change-Id: Ib09c121471bd8c490442330a478145a7d1d8855f
Signed-off-by: Naresh G Solanki <naresh.solanki@intel.com>
Reviewed-on: https://review.coreboot.org/16538
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/drivers/intel/fsp2_0/include/fsp/api.h

@@ -14,6 +14,7 @@
 #define _FSP2_0_API_H_
 
 #include <stddef.h>
+#include <stdint.h>
 #include <fsp/soc_binding.h>
 
 #define FSP_SUCCESS	EFI_SUCCESS