ARM: tango: Improve ARCH_MULTIPLATFORM compatibility

Calling platform-specific code unconditionally blows up when running
an ARCH_MULTIPLATFORM kernel on a different platform. Don't do it.

Reported-by: Paolo Pisati <p.pisati@gmail.com>
Signed-off-by: Marc Gonzalez <marc.w.gonzalez@free.fr>
Acked-by: Pavel Machek <pavel@ucw.cz>
Cc: stable@vger.kernel.org # v4.8+
Fixes: a30eceb7 ("ARM: tango: add Suspend-to-RAM support")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>