Since the tty layer now takes care of user space writes,
__uart_user_write() and associated temporary buffer and temporary
buffer semaphore have all become unnecessary.  There's also little
point in having __uart_kern_write() separate from uart_write(), so
combine the two together.

Adrian Bunk kindly provided the patch to remove __uart_user_write().
The rest of the work is rmk's.

Signed-off-by: Adrian Bunk
Signed-off-by: Russell King <rmk@arm.linux.org.uk>