vgapci: Use vga_pci_alloc_resource() to map PCI Expansion ROM

This is cleaner and fixes Video BIOS mapping when the given device isn't
the boot display.

Submitted by:	jhb@
Approved by:	re (kib)
drm/radeon: Fix usage of vga_pci_map_bios()

vga_pci_(un)map_bios() takes a vgapci device as argument, not a drmn
one. This fixes a bug where the BIOS couldn't be mapped if the device
wasn't the boot display.

Approved by:	re (kib; blanket for following drm2/radeon commits)
drm/radeon: Fix usage of pci_save_state() and pci_restore_state()

Calling those functions with the drmn device as argument causes a panic,
because it's not a direct child of pci$N. They must be called with the
vgapci device instead.

This fix is not enough to make suspend/resume work reliably.

Approved by:	re (blanket)
Pull the hyperv drivers from GENERIC until the fix to the disengage
driver to make it only probe when running on hyperv is reviewed and
tested.

Approved by:	re (rodrigc)
Minor mdoc fixes.

Approved by:	re (blanket)
Properly remove c++filt.

The c++filt binary is only installed if ${MK_GCC} == yes && ${MK_CXX} ==
yes. This means that it should be removed if ${MK_GCC} == no ||
${MK_CXX} == no. In its current form, it actually uses a conjunction
instead of a disjunction.

As there is already a separate block for ${MK_CXX} == no listing
c++filt, simply remove the conditional entirely.

Approved by:	re (gjb)
Merge branch 'master' of https://github.com/freebsd/freebsd