SPARSE_IRQ is required for single zImage support.

With this enabled, we can delete <mach/irqs.h>. This requires removing
one unnecessary include of that file, and hard-coding the PCIe IRQ into
the PCIe driver. This is a hack that will be dealt with as part of
converting the PCIe driver into a true DT-supporting driver.
Signed-off-by: Stephen Warren <swarren@nvidia.com>