qemu: update the PCI(e) docs

qemu: update the PCI(e) docs

A little update to the PCI(e) docs. The PCI wiki article has been
reworked as well, in line with changes from this patch.

Along some minor grammar fixes added:
 * how to check if kernel modules are being loaded
 * how to check which drivers to blacklist
 * how to add softdeps for module loading
 * where to find kernel params

Signed-off-by: Noel Ullreich <n.ullreich@proxmox.com>
 [ TL: squash in dropping two trailing whitespace errors ]
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>