This patch enables handling PMU overflow IRQ by GIC SPI's
directly in EL3. Also implement additional SMC routine,
which can disable the solution on demand in runtime.

Since it is possible to configure PMU interrupt trigger type
in the MADT ACPI table, it is enough to set it only once in EL3
during initialization.

Change-Id: Ie76aa62ccc4fd7cabfec9e3d5ed9970ada1c1b2a
Signed-off-by: Marcin Wojtas <mw@semihalf.com>
Reviewed-by: Kostya Porotchkin <kostap@marvell.com>