fix(stm32mp1): include assert.h to fix build failure

stm32mp1 platform build failed with the error [1] in the coverity, to
fix it included assert.h file.

Including bl32/sp_min/sp_min.mk
plat/st/stm32mp1/plat_image_load.c: In function
'plat_get_bl_image_load_info':
plat/st/stm32mp1/plat_image_load.c:30:2: error: implicit declaration of
function 'assert' [-Werror=implicit-function-declaration]
   30 |  assert(bl33 != NULL);
      |  ^~~~~~
plat/st/stm32mp1/plat_image_load.c:9:1: note: 'assert' is defined in
header '<assert.h>'; did you forget to '#include <assert.h>'?
    8 | #include <plat/common/platform.h>
  +++ |+#include <assert.h>
    9 |
cc1: all warnings being treated as errors

Signed-off-by: Manish V Badarkhe <manish.badarkhe@arm.com>
Change-Id: I486bd695298798c05008158545668020babb3eca

plat/st/stm32mp1/plat_image_load.c

@@ -4,6 +4,8 @@
  * SPDX-License-Identifier: BSD-3-Clause
  */
 
+#include <assert.h>
+
 #include <common/desc_image_load.h>
 #include <plat/common/platform.h>