PM: hibernate: Add pm_hibernation_mode_is_suspend()

Some drivers have different flows for hibernation and suspend. If
the driver opportunistically will skip thaw() then it needs a hint
to know what is happening after the hibernate.

Introduce a new symbol pm_hibernation_mode_is_suspend() that drivers
can call to determine if suspending the system for this purpose.

Tested-by: Ionut Nechita <ionut_n2001@yahoo.com>
Tested-by: Kenneth Crudup <kenny@panix.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Mario Limonciello (AMD) <superm1@kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>