Now that __initmv references the machvec section unconditionally
there have been cases where folks have been mistakenly flagging
non-machvec structures with the machvec section attribute (presumably
to shut up modpost). This leads to obscure breakage in earlyprintk
amongst other places and is rather non-obvious.

Add a simple sanity check to try and catch __initmv misuse and
panic early.
Reported-by: NMarkus Brunner <super.firetwister@gmail.com>
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>

This kills off the BareCPU board as a "special" machvec, rather,
we leave this as a default for when no other vector is available,
or when we want to use it in combination with other vectors for
testing with generic ops. As sh_mv is copied out anyways (or
overloaded when an alternate vector is explicitly selected), this
doesn't consume any additional memory.

The generic machvec can be forcibly selected with sh_mv=generic,
or by not having any other boards enabled.
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>

We now throw all of the machvecs in to .machvec.init and either
select one on the command line, or copy out the first (and
usually only) one to sh_mv. The rest are freed as usual.

This gets rid of all of the silly sh_mv aliasing and makes the
selection explicit rather than link-order dependent.
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>

This fixes up much of the machvec handling, allowing for it to be
overloaded on boot. Making practical use of this still requires
some Kconfig munging, however.
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>