drivers: firmware: psci: Announce support for OS initiated suspend mode

PSCI firmware v1.0+, supports two different modes for CPU_SUSPEND.
The Platform Coordinated mode, which is the default and mandatory
mode, while support for the OS initiated (OSI) mode is optional.

In some cases it's interesting for the user/developer to know if
the OSI mode is supported by the PSCI FW, so print a message to
the log if that is the case.

Co-developed-by: Lina Iyer <lina.iyer@linaro.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>