mfi(4): Add D_MPSAFE to the disk flags.

When porting it, I didn't know that this is indicated by the _absence_
of DISKFLAG_NEEDSGIANT.

Tested-by: ftigeot
ccdconfig(8): When ccd can't be kldloaded, explain a possible reason.

If /etc/ccd.conf is present, /etc/rc.d/ccd will run ccdconfig in the
early boot when only root is mounted read-only. On HAMMER systems (or
any other system where /boot isn't part of the root partition) it can
not automatically load ccd.ko at this point. This was different on
UFS where /boot was usually not separate.

So in case it fails, give the user a better message that explains the
options he has.

Dragonfly-bug: <http://bugs.dragonflybsd.org/issues/2439>
Reported-by:   Christer Solskogen
kernel: A few small fixes to make a minimal kernel config compile.

It is solely for my build testing purposes:

platform        pc64
machine         x86_64
machine_arch    x86_64
ident           MINI
cpu             HAMMER_CPU

* Put two INET specific functions in uipc_socket.c under #ifdef INET.

* Compile in isa_intr.c only when isa is specified in the config.

* Move PCI specific include under #if 0 too in mp_clock.c

* In nexus.c, compile in PCI specific parts only when pci is
  specified in the config.
kernel: Move some externs under INET too.