msm: board-8916: Add a dedicated DT_MACHINE for 8936

Add a new DT_MACHINE for 8936 in board-8916 to share the same
binary, which could support dynamic selection of correct
DT_MACHINE in runtime according to device tree.

Change-Id: I9f991e8421dac819eaa8b58b1474bcca5b5ad46f
Signed-off-by: Xiaocheng Li <lix@codeaurora.org>