Nokia RX-51: Fix double space key press

Space key is indicated by two different bits. Some HW models indicate press
of space key only by the first bit. Qemu indicates it by both bits at the
same time, which is currently interpreted by u-boot as double key press.

Fix this issue by setting first bit when only second is set (to support HW
models which indicate press only by second bit) and always clearing second
bit before processing to not report double space key press.

Signed-off-by: Pali Rohár <pali@kernel.org>