feat(msm8916): power on L2 caches for secondary clusters

On platforms with multiple CPU clusters the L2 cache will be only on
for the cluster of the boot CPU. Add the necessary sequence to power it
up for secondary clusters similar to the CPU boot sequence.

No functional change for platforms with a single cluster. The new code
is discarded entirely in this case.

Change-Id: I3d3bce519a8a10ef5278d74d81acf59123e00454
Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
diff --git a/plat/qti/msm8916/msm8916_pm.h b/plat/qti/msm8916/msm8916_pm.h
index 38190a3..f301d3c 100644
--- a/plat/qti/msm8916/msm8916_pm.h
+++ b/plat/qti/msm8916/msm8916_pm.h
@@ -8,5 +8,6 @@
 #define MSM8916_PM_H
 
 void msm8916_cpu_boot(uintptr_t acs);
+void msm8916_l2_boot(uintptr_t base);
 
 #endif /* MSM8916_PM_H */