msm: 8916: Move dts into a subdirectory

This makes locating our files less convoluted, since the
arch/arm/boot/dts directory is now quite bloated.

Change-Id: I9b6d4149bba3d1021d4d15890f2db02f95a51507
Signed-off-by: Abhimanyu Kapur <abhimany@codeaurora.org>