msm: pcie: support PCIe enumeration via wake IRQ

Some PCIe endpoint will fail the PCIe enumeration during AP side
bootup, and will trigger wake IRQ to AP side when it is up. Thus,
add the support for this kind of enumeration via wake IRQ only.

CRs-fixed: 660202
Change-Id: I643d5e73bbbe5b7574047172206afb4f20d68a3c
Signed-off-by: Yan He <yanhe@codeaurora.org>