alpha: kernel: using memcpy() instead of strcpy()

When sending message in send_secondary_console_msg(), the length is not
include the NUL byte, and also not copy NUL to 'ipc_buffer'.

When receive message in recv_secondary_console_msg(), the 'cnt' also
excludes NUL.

So when get string from ipc_buffer, it may not be NUL terminated.

Then use memcpy() instead of strcpy(), and set last byte NUL.

Reviewed-by: Matt Turner <mattst88@gmail.com>
Signed-off-by: Matt Turner <mattst88@gmail.com>
Signed-off-by: Chen Gang <gang.chen@asianux.com>