zephyr: shell: Fix implicit declaration of function 'strtol'

Fix implicit declaration of function 'strtol' by including
zephyr/shell/shell_string_conv.h.

Signed-off-by: Jyri Sarha <jyri.sarha@linux.intel.com>

Author: Jyri Sarha

zephyr/sof_shell.c

@@ -11,6 +11,7 @@
 #include <zephyr/kernel.h>
 #include <zephyr/sys/printk.h>
 #include <zephyr/shell/shell.h>
+#include <zephyr/shell/shell_string_conv.h>
 
 #define SOF_TEST_INJECT_SCHED_GAP_USEC 1500