Musca S1: include missing cmsis_nvic.h

The vector table needs to be copied from ROM to RAM, in order for us
to set IRQ handlers at run time. The address in RAM is defined by
`NVIC_RAM_VECTOR_ADDRESS` in `cmsis_nvic.h`, but its inclusion
was missing from Musca S1's `cmsis.h` and consequently the vector
table was not copied.

On most targets this results in a memory access error when we set
vectors. But Musca S1's ROM is in its MRAM (which can be accessed
like any RAMs), and this causes the ROM image to be modified
with no error/warning. On the next boot, MCUboot fails the image
integrity check.

This commit adds the missing include, in the same spirit as
01dd997.

Author: LDong-Arm

targets/TARGET_ARM_SSG/TARGET_MUSCA_S1/device/cmsis.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017-2019 Arm Limited. All rights reserved.
+ * Copyright (c) 2017-2021 Arm Limited. All rights reserved.
  *
  * SPDX-License-Identifier: Apache-2.0
  *
@@ -83,4 +83,6 @@
   #warning Not supported compiler type
 #endif
 
+#include "cmsis_nvic.h"
+
 #endif /*__MUSCA_S1_CMSIS_H__ */