PCI: imx6: Convert to NOIRQ_SYSTEM_SLEEP_PM_OPS()

Replace SET_NOIRQ_SYSTEM_SLEEP_PM_OPS() with NOIRQ_SYSTEM_SLEEP_PM_OPS(),
which has the advantage that the compiler always sees the PM callbacks as
referenced, so they don't need to be wrapped with "#ifdef CONFIG_PM_SLEEP"
or tagged with "__maybe_unused" to avoid "defined but not used" warnings.

See 1a3c7bb0 ("PM: core: Add new *_PM_OPS macros, deprecate old ones").

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>