winsys/radeon: Unmap GPU VM address range when destroying BO

winsys/radeon: Unmap GPU VM address range when destroying BO

But only when doing so is safe according to the
RADEON_INFO_VA_UNMAP_WORKING kernel query.

This avoids kernel GPU VM address range conflicts when the BO has other
references than the GEM handle being closed, e.g. when the BO is shared.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=90537
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=90873

Cc: "10.5 10.6" <mesa-stable@lists.freedesktop.org>
Reviewed-by: Christian König <christian.koenig@amd.com>