cortex_m: make bit fields in cortex_m unsigned.

cortex_m: make bit fields in cortex_m unsigned.

Expression like (0xffff << 16) evaluate to type int, which is not able
to hold that value, producing a warning when compiling with
-fsanitize=undefined. This patch makes most of the cortex_m constants
unsigned using the BIT() macro or appending "ul" when possible to fix
the undefined behavior warning.

Signed-off-by: iosabi <iosabi@protonmail.com>
Change-Id: I7af194305ef612d7a32e74eaf9f11dd85fa87f32
Reviewed-on: http://openocd.zylin.com/5583
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-by: Christopher Head <chead@zaber.com>
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>