Introduce new sized integer typedefs

This is a start to move away from the C99 {u}int{8,16,32,64}_t types to
Zephyr defined u{8,16,32,64}_t and s{8,16,32,64}_t.  This allows Zephyr
to define the sized types in a consistent manor across all the
architectures we support and not conflict with what various compilers
and libc might do with regards to the C99 types.

We introduce <zephyr/types.h> as part of this and have it include
<stdint.h> for now until we transition all the code away from the C99
types.

We go with u{8,16,32,64}_t and s{8,16,32,64}_t as there are some
existing variables defined u8 & u16 as well as to be consistent with
Zephyr naming conventions.

Jira: ZEP-2051

Change-Id: I451fed0623b029d65866622e478225dfab2c0ca8
Signed-off-by: Kumar Gala <kumar.gala@linaro.org>

arch/arm/core/cortex_m/prep_c.c

@@ -17,7 +17,7 @@
  */
 
 #include <kernel.h>
-#include <stdint.h>
+#include <zephyr/types.h>
 #include <toolchain.h>
 #include <linker-defs.h>
 #include <nano_internal.h>