ARM: msm: Move MSM's DT based hardware to multi-platform support

The DT based MSM platforms can join the multi-platform builds, so
introduce a DT based ARCH_MSM option. This option allows DT based
MSM platforms to be built into the multi-platform kernel. Also
introduce a hidden ARCH_MSM config that both the DT and non-DT
platform support code select to avoid churn in places that depend
on CONFIG_ARCH_MSM.

Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Olof Johansson <olof@lixom.net>