parisc: Define O_NONBLOCK to become 000200000

HPUX has separate NDELAY & NONBLOCK values. In the past we wanted to
be able to run HP-UX binaries natively on parisc Linux which is why
we defined O_NONBLOCK to 000200004 to distinguish NDELAY & NONBLOCK
bits.
But with 2 bits set in this bitmask we often ran into compatibility
issues with other Linux applications which often only test one bit (or
even compare the values).

To avoid such issues in the future, this patch changes O_NONBLOCK to
become 000200000. That way old programs will still be functional, and
for new programs we now have only one bit set.

Update the comment about SOCK_NONBLOCK too.

Signed-off-by: Helge Deller <deller@gmx.de>