feat(qemu): enable FEAT_ECV when present

QEMU supports FEAT_ECV since commit 2808d3b38a52 ("target/arm: Implement
FEAT_ECV CNTPOFF_EL2 handling"), in the v9.0.0 release. Enable
auto-detecting the feature on the QEMU platforms, in order to set
SCR.ECVEN. Without this, EL2 gets undefined instruction exceptions when
trying to access the new CNTPOFF register.

Change-Id: I555a5f9a9a84fd23e64ca85219ed1599204c6bb2
Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
diff --git a/plat/qemu/common/common.mk b/plat/qemu/common/common.mk
index 16187ef..8142599 100644
--- a/plat/qemu/common/common.mk
+++ b/plat/qemu/common/common.mk
@@ -114,6 +114,7 @@
 ENABLE_FEAT_SB		:=	0
 
 # 8.6
+ENABLE_FEAT_ECV		:=	2
 ENABLE_FEAT_FGT		:=	2
 
 # 8.7