cosmetic: Remove trailing whitespaces

No functional change, just remove whitspace at end-of-line.
IRQ handler: Support IRQ sharing and use ioread/iowrite routines

Return IRQ_NONE from interrupt handler when no action was taken. This
allows the kernel to detect spurious interrupts and allows dyplo to
share its IRQ with other devices.

Use ioread32 and iowrite32 to perform memory operations instead of plain
memory mapped access.