pciehp: Fix wrong slot capability check

Current pciehp saves only 8bits of Slot Capability registers in
ctrl->ctrlcap. But it refers more than 8bit for checking EMI capability.
It is clearly a bug and EMI would never work. To fix this problem,
this patch saves full Slot Capability contens in ctrl->slot_cap. It also
reduce the redundant reads of Slot Capability register. And this pach
also cleans up the macros to check the slot capabilitys (e.g. MRL_SENS(),
and so on).

Signed-off-by: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Signed-off-by:  Kristen Carlson Accardi <kristen.c.accardi@intel.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>