soc: stm32: fix pm_s2ram linker warning

Below warning is reported in Zephyr upstream weekly CI after
34985a7 was merged:
```
ld.bfd: warning: orphan section .TEXT.pm_s2ram_mark_check_and_clear'
from zephyr/libzephyr.a(s2ram_marking.S.obj)' being placed in section
`.TEXT.pm_s2ram_mark_check_and_clear'
```

Fix the warning by adding the appropriate headers.

Signed-off-by: Anjali Kashyap <anjkas23@gmail.com>

Author: 0xAnjali

soc/st/stm32/stm32wb0x/s2ram_marking.S

@@ -12,6 +12,7 @@
 #include <offsets_short.h>
 #include <zephyr/arch/cpu.h>
 #include <zephyr/arch/common/pm_s2ram.h>
+#include <zephyr/linker/sections.h>
 
 /* Read RCC and PWRC base from Device Tree */
 #include <zephyr/devicetree.h>