irqchip/riscv-imsic: Improve IOMMU DMA support

We have a separate RISC-V IMSIC MSI address for each CPU so changing
MSI (or IRQ) affinity results in re-programming of MSI address in
the PCIe (or platform) device.

Currently, the iommu_dma_prepare_msi() is called only once at the
time of IRQ allocation so IOMMU DMA domain will only have mapping
for one MSI page. This means iommu_dma_compose_msi_msg() called
by imsic_irq_compose_msi_msg() will always use the same MSI page
irrespective to target CPU MSI address. In other words, changing
MSI (or IRQ) affinity for device using IOMMU DMA domain will not
work.

To address the above issue, we do the following:
1) Map MSI pages for all CPUs in imsic_irq_domain_alloc()
   using iommu_dma_prepare_msi().
2) Extend iommu_dma_compose_msi_msg() to lookup the correct
   msi_page whenever the msi_page stored as iommu cookie
   does not match.

Reported-by: Vincent Chen <vincent.chen@sifive.com>
Signed-off-by: Anup Patel <apatel@ventanamicro.com>