arch: arm: cortex_m: add memory to the clobber list

Add "memory" to the clobber list"

From GCC 14 the compiler optimizes away memory accesses that do not
impact the asm block. Adding the memory to the clobber list lets the
compiler know that the memory state is to be preserved.

Signed-off-by: Wilfried Chauveau <wilfried.chauveau@arm.com>
Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>