e1000e: If ASPM L0s needs to be disabled, do it prior to enabling device

e1000e: If ASPM L0s needs to be disabled, do it prior to enabling device

Based on a patch from Naga Chumbalkar <nagananda.chumbalkar@hp.com>:

If ASPM L0s needs to be disabled due to HW errata, do it prior to
"enabling" the device. This way if the kernel ever defaults its
aspm_policy to POLICY_POWERSAVE, then the e1000e driver will get a
chance to disable ASPM on the misbehaving device *prior* to calling
pci_enable_device_mem(). This will be useful in situations
where the BIOS indicates ASPM support on the server by clearing the
ACPI FADT "ASPM Controls" bit.

Note:
The kernel (2.6.38) currently uses the BIOS "default" as its aspm_policy.
However, Linux distros can diverge from that and set the default to
"powersave".

v2: o cleanup namespace pollution of e1000e_disable_aspm(),
    o fix type and initialization of the new aspm_disable_flag in a few
      functions, and
    o redefine FLAG2_DISABLE_ASPM_L0S to the first unused bit in
      adapter->flags2.

Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Cc: Naga Chumbalkar <nagananda.chumbalkar@hp.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>