e1000e: Fix a compile flag mis-match for suspend/resume

This patch addresses a mis-match between the declaration and usage of
the e1000_suspend and e1000_resume functions.  Previously, these
functions were declared in a CONFIG_PM_SLEEP wrapper, and then utilized
within a CONFIG_PM wrapper.  Both the declaration and usage will now be
contained within CONFIG_PM wrappers.

Signed-off-by: Dave Ertman <davidx.m.ertman@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>