ARM: msm: Properly switch secondary CPUs into THUMB2 mode

The kernel is always entered into in ARM mode to keep things
simple. The secondary CPU entry points were assuming that the
kernel is always compiled for ARM mode but it's possible to
compile the kernel for THUMB2 mode. Switch into THUMB2 mode as
early as possible in the secondary CPU entry points.

Change-Id: I918c207ea167d044ab3552b6ea608d3b9f2fbcf6
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>