sparc: kernel: using strlcpy() instead of strcpy()

'boot_command_line' and 'full_boot_str' has a fix length, 'cmdline_p' and
'boot_command' maybe larger than them. So use strlcpy() instead of strcpy()
to avoid memory overflow.

Signed-off-by: Zhao Hongjiang <zhaohongjiang@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>