iwlwifi: pcie: always disable L0S states

L0S states have been found to be unstable with our devices and in
newer hardware they are not supported at all, so we must always set
the L0S_DISABLED bit.  Previously we were only disabling L0S states if
L1 was supported, because the assumption was that transitions from L0S
to L1 state was the problematic case.  But now we should never use
L0S, so do it regardless of whether L1 is supported or not.

Signed-off-by: Luca Coelho <luciano.coelho@intel.com>