ARM: OMAP2+: Disable code that currently does not work with multiplaform

ARM: OMAP2+: Disable code that currently does not work with multiplaform

We still need to fix up few places for multiplatform support,
but that can proceed separately. Fix the issue by making the
problem drivers depends !ARCH_MULTIPLATFORM for now.

The remaining pieces that are not multiplatform compatible
for omap2+ SoCs are:

1. Some drivers are using custom omap_dm_timer calls

There are two drivers that are directly usign omap hardware
timers for PWM and DSP clocking: drivers/media/rc/ir-rx51.c and
drivers/staging/tidspbridge/core/dsp-clock.c. These can be
fixed for multiplatform by allowing a minimal set of hardware
timers to be accessed, and for some functionality by using the
hrtimer framework.

2. Hardware OMAP4_ERRATA_I688 needs to be fixed up

This can't be enabled for multiplatform configurations in
it's current form. It may be possible to fix it up to do
instruction replacement early on during init. Luckily it
looks like this errata does not seem to get hit with
mainline kernel code alone at least currently.

3. Legacy header needed for omap-sham.c

Looks like it still needs mach/irqs.h for omap1 that
does not exist for multiplatform systems. Just ifdef
it for now.

4. Mailbox is waiting to get moved to drivers

Disable it for now to avoid adding a dependency to the
mailbox patches.

Cc: Timo Kokkonen <timo.t.kokkonen@iki.fi>
Cc: Sean Young <sean@mess.org>
Cc: "Víctor Manuel Jáquez Leal" <vjaquez@igalia.com>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Mauro Carvalho Chehab <mchehab@redhat.com>
Cc: Omar Ramirez Luna <omar.ramirez@ti.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Santosh Shilimkar <santosh.shilimkar@ti.com>
Tested-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
[tony@atomide.com: updated to disable mailbox]
Signed-off-by: Tony Lindgren <tony@atomide.com>