e1000e / igb / PM: Eliminate CONFIG_PM_RUNTIME

After commit b2b49ccb (PM: Kconfig: Set PM_RUNTIME if PM_SLEEP is
selected) PM_RUNTIME is always set if PM is set, so #ifdef blocks
depending on CONFIG_PM_RUNTIME within #ifdef blocks depending on
CONFIG_PM may be dropped now.

Do that in the e1000e and igb network drivers.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>