vfio: fix mapping of MSIX bar

vfio: fix mapping of MSIX bar

VFIO virtualizes MSIX table for the guest but not mapping the part of
a BAR which contains an MSIX table. Since vfio_mmap_bar() mmaps chunks
before and after the MSIX table, they have to be aligned to the host
page size which may be TARGET_PAGE_MASK (4K) or 64K in case of PPC64.

This fixes boundaries calculations to use the real host page size.

Without the patch, the chunk before MSIX table may overlap with the MSIX
table and mmap will fail in the host kernel. The result will be serious
slowdown as the whole BAR will be emulated by QEMU.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>