fs/xfs remove obsolete simple_strto<foo>

This patch replaces usages of obsolete simple_strtoul with kstrtoint in
xfs_args and suffix_strtoul.

Signed-off-by: Abhijit Pawar <abhi.c.pawar@gmail.com>
Reviewed-by: Jie Liu <jeff.liu@oracle.com>
Signed-off-by: Ben Myers <bpm@sgi.com>