msm: ep_pcie: Avoid polling for ltssm state if perst is asserted

Device polls for ltssm state by reading PCIE status register as part
of ep_pcie_core_enable_endpoint. If it receives a perst assertion
event during polling, device completes polling and then handles perst
assertion with the existing logic. But polling for ltssm state is not
necessary here as the L0 link state is not possible after perst
assertion. This delays the handling of perst assertion and subsequent
perst deaasertion events.

To avoid this delay, avoiding polling for ltssm state if perst is
asserted. Added check for perst during polling of ltssm state and
breaking the loop if perst is asserted.

Change-Id: I38dc82070749751cfd14661ac95eb95eb8dcb665
Signed-off-by: Sai Chaitanya Kaveti <quic_skaveti@quicinc.com>