msm: 9615: Select MIGHT_HAVE_L2X0

With the 3.4 merge, the way L2X0 config is selected changed.
(It no longer does the depends on ...). Select the missing
L2X0 config for 9615 to make sure we are using the external
L2 cache.

Change-Id: I5dc8bb53b6de8d795347876056bf6e2f7f88ed43
Signed-off-by: Rohit Vaswani <rvaswani@codeaurora.org>