PCI: Default PCIe ASPM control to on and require !EMBEDDED to disable

The CONFIG_PCIEASPM option is confusing and potentially dangerous. ASPM is
a hardware mediated feature rather than one under direct OS control, and
even if the config option is disabled the system firmware may have turned
on ASPM on various bits of hardware. This can cause problems later -
various hardware that claims to support ASPM does a poor job of it and may
hang or cause other difficulties. The kernel is able to recognise this in
many cases and disable the ASPM functionality, but only if CONFIG_PCIEASPM
is enabled.

Given that in its default configuration this option will either leave the
hardware as it was originally or disable hardware functionality that may
cause problems, it should by default y. The only reason to disable it
ought to be to reduce code size, so make it dependent on CONFIG_EMBEDDED.

Signed-off-by: Matthew Garrett <mjg@redhat.com>
Cc: lrodriguez@atheros.com
Cc: maximlevitsky@gmail.com
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>