soc: qcom: spm: Fix idle on THUMB2 kernels

The ifc6410 firmware always enters the kernel in ARM state from
deep idle. Use the cpu_resume_arm() wrapper instead of
cpu_resume() to property switch into the THUMB2 state when we
wake up from idle.

This fixes a problem reported by Kevin Hilman on next-20150601
where the ifc6410 fails to boot a THUMB2 kernel because the
platform's firmware always enters the kernel in ARM mode from
deep idle states.

Reported-by: Kevin Hilman <khilman@linaro.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Lina Iyer <lina.iyer@linaro.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Kevin Hilman <khilman@linaro.org>