target-arm: Enable vPMU support under TCG mode

This patch contains several fixes to enable vPMU under TCG mode. It
first removes the checking of kvm_enabled() while unsetting
ARM_FEATURE_PMU. With it, the .pmu option can be used to turn on/off vPMU
under TCG mode. Secondly the PMU node of DT table is now created under TCG.
The last fix is to disable the masking of PMUver field of ID_AA64DFR0_EL1.

Signed-off-by: Wei Huang <wei@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1486504171-26807-5-git-send-email-wei@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>