ARM: msm: Only compile io.c on platforms that use it

Only the non-dt based MSM platforms need to map memory from their
machine descriptor. Unfortunately it is always compiled if
ARCH_MSM=y and the file also has mach/ includes in it. Since
dt-based MSM platforms aren't actually using anything in this
file just compile io.c on the non-dt based MSM platforms. This
allows the dt-based platforms to participate in the
multi-platform kernel.

Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: David Brown <davidb@codeaurora.org>