refactor(cpufeat): rename ENABLE_SPE_FOR_LOWER_ELS to ENABLE_SPE_FOR_NS

At the moment we hardcode the SPE functionality to be available on the
non-secure side only, by setting MDCR_EL2.E2PB accordingly.

This should be reflected in the feature selection symbol, so rename that
to ENABLE_SPE_FOR_NS, to make it clearer that SPE is not supported in
the secure world.

Change-Id: I3f9b48eab1a45d6ccfcbb9c90a11eeb66867ad9a
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
diff --git a/plat/qti/msm8916/platform.mk b/plat/qti/msm8916/platform.mk
index e516cea..60fb25d 100644
--- a/plat/qti/msm8916/platform.mk
+++ b/plat/qti/msm8916/platform.mk
@@ -44,7 +44,7 @@
 
 # Disable features unsupported in ARMv8.0
 ENABLE_AMU			:= 0
-ENABLE_SPE_FOR_LOWER_ELS	:= 0
+ENABLE_SPE_FOR_NS		:= 0
 ENABLE_SVE_FOR_NS		:= 0
 
 # MSM8916 uses ARM Cortex-A53 r0p0 so likely all the errata apply