MIPS: Alchemy: drop DB1000 IrDA support bits

The IrDA drivers are gone, drop the now unused DB1000 board
support for it.

Signed-off-by: Manuel Lauss <manuel.lauss@gmail.com>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: Linux-MIPS <linux-mips@vger.kernel.org>