All the board types can use IRQ 2-7 for async command support. Remove
the 'IRQbits', which is a mask of the valid IRQs, from the boardinfo
and refactor pcl816_attach().
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com> Reviewed-by: Ian Abbott <abbotti@mev.co.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>