Suspend: Introduce begin() and end() callbacks

On ACPI systems the target state set by acpi_pm_set_target() is
reset by acpi_pm_finish(), but that need not be called if the
suspend fails.  All platforms that use the .set_target() global
suspend callback are affected by analogous issues.

For this reason, we need an additional global suspend callback that
will reset the target state regardless of whether or not the suspend
is successful.  Also, it is reasonable to rename the .set_target()
callback, since it will be used for a different purpose on ACPI
systems (due to ACPI 1.0x code ordering requirements).

Introduce the global suspend callback .end() to be executed at the
end of the suspend sequence and rename the .set_target() global
suspend callback to .begin().

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Len Brown <len.brown@intel.com>