ARM: STi: STiH407: Enable PMU IRQs

This driver is used to enable System Configuration Register controlled
External, CTI (Core Sight), PMU (Performance Management), and PL310 L2
Cache IRQs prior to use.

Here we are enabling PMU IRQs on both channels.

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Maxime Coquelin <maxime.coquelin@st.com>