toolchain/gcc: Add UNALIGNED_GET macro

Similar to PACK_STRUCT it provide safe access to possible unaligned data
but it is much more convenient to use with non-struct types since all
one need to do is add a cast e.g. UNALIGNED_GET((uint16_t *) data).

Change-Id: I46402bdf1dd13081fe340a7214a84750a6cf04d2
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

include/toolchain/gcc.h

@@ -87,6 +87,15 @@
 	while (0)
 #endif /* !CONFIG_UNALIGNED_WRITE_UNSUPPORTED */
 
+/* Unaligned access */
+#define UNALIGNED_GET(p)						\
+__extension__ ({							\
+	struct  __attribute__((__packed__)) {				\
+		__typeof__(*(p)) __v;					\
+	} *__p = (__typeof__(__p)) (p);					\
+	__p->__v;							\
+})
+
 #define _GENERIC_SECTION(segment) __attribute__((section(#segment)))
 
 #define PACK_STRUCT     __attribute__((__packed__))