core: fix compiling error if reserved SHM not used

Fix compiling error when only use dynamic shared memory
(i.e: CFG_CORE_DYN_SHM=y && CFG_CORE_RESERVED_SHM=n) with
CFG_SHMEM_START and CFG_SHMEM_SIZE not defined.

Reviewed-by: Jens Wiklander <jens.wiklander@linaro.org>
Signed-off-by: Fangsuo Wu <fangsuowu@asrmicro.com>
diff --git a/core/arch/arm/mm/core_mmu.c b/core/arch/arm/mm/core_mmu.c
index 866d53b..ad1e579 100644
--- a/core/arch/arm/mm/core_mmu.c
+++ b/core/arch/arm/mm/core_mmu.c
@@ -1276,9 +1276,11 @@
 	case CORE_MEM_TA_RAM:
 		return core_is_buffer_inside(pbuf, len, TA_RAM_START,
 							TA_RAM_SIZE);
+#ifdef CFG_CORE_RESERVED_SHM
 	case CORE_MEM_NSEC_SHM:
 		return core_is_buffer_inside(pbuf, len, TEE_SHMEM_START,
 							TEE_SHMEM_SIZE);
+#endif
 	case CORE_MEM_SDP_MEM:
 		return pbuf_is_sdp_mem(pbuf, len);
 	case CORE_MEM_CACHED: