meson/gxl: Configure and boot SCP

On Amlogic gxl (s905x) SOC, in order to use SCP, bl31 has to send bl30
and bl301 firmware along with their SHA256 hash over scpi.

Signed-off-by: Remi Pommarel <repk@triplefau.lt>
diff --git a/plat/meson/gxl/gxl_private.h b/plat/meson/gxl/gxl_private.h
index 910a42c..913cbf6 100644
--- a/plat/meson/gxl/gxl_private.h
+++ b/plat/meson/gxl/gxl_private.h
@@ -8,6 +8,7 @@
 #define GXBB_PRIVATE_H
 
 #include <stdint.h>
+#include <stddef.h>
 
 /* Utility functions */
 unsigned int plat_gxbb_calc_core_pos(u_register_t mpidr);
@@ -29,6 +30,7 @@
 uint32_t scpi_efuse_read(void *dst, uint32_t base, uint32_t size);
 void scpi_unknown_thermal(uint32_t arg0, uint32_t arg1,
 			  uint32_t arg2, uint32_t arg3);
+void scpi_upload_scp_fw(uintptr_t addr, size_t size, int send);
 
 /* Peripherals */
 void gxbb_thermal_unknown(void);