ARM: qcom: Split Qualcomm support into legacy and multiplatform

Introduce a new mach-qcom that will support SoCs that intend to be
multiplatform compatible while keeping mach-msm to legacy SoC/board
support that will not transition over to multiplatform.

As part of this, we move support for MSM8X60, MSM8960 and MSM8974 over
to mach-qcom.

Signed-off-by: Kumar Gala <galak@codeaurora.org>