dts: add missing m8 dtsi's

Change-Id: Id5af094e567bd987a531018d8e9220790aca6b86
arm: mach-msm: board-htc-8974: import m8whl (Sprint) and w8wl (VZW) variant

Change-Id: Ie92eee3c7bfdf8ccc260b07a6691198885d38ab0