MVBLUE: Remove CONFIG_CMD_IRQ

Neither the MVBLUE nor its underlying architecture implement the
do_irqinfo() function which is required when CONFIG_CMD_IRQ is defined.
This change fixes the following MVBLUE compiler error:

-> ./MAKEALL MVBLUE
Configuring for MVBLUE board...
common/libcommon.a(cmd_irq.o):(.u_boot_cmd+0x24): undefined reference to `do_irqinfo'
make: *** [u-boot] Error 1

Signed-off-by: Peter Tyser <ptyser@xes-inc.com>
Acked-by: Andre Schwarz <andre.schwarz@matrix-vision.de>