PCI: qcom-ep: Move controller cleanups to qcom_pcie_perst_deassert()

In the Linux kernel, the following vulnerability has been resolved:

PCI: qcom-ep: Move controller cleanups to qcom_pcie_perst_deassert()

Currently, the endpoint cleanup function dw_pcie_ep_cleanup() and EPF
deinit notify function pci_epc_deinit_notify() are called during the
execution of qcom_pcie_perst_assert() i.e., when the host has asserted
PERST#. But quickly after this step, refclk will also be disabled by the
host.

All of the Qcom endpoint SoCs supported as of now depend on the refclk from
the host for keeping the controller operational. Due to this limitation,
any access to the hardware registers in the absence of refclk will result
in a whole endpoint crash. Unfortunately, most of the controller cleanups
require accessing the hardware registers (like eDMA cleanup performed in
dw_pcie_ep_cleanup(), powering down MHI EPF etc...). So these cleanup
functions are currently causing the crash in the endpoint SoC once host
asserts PERST#.

One way to address this issue is by generating the refclk in the endpoint
itself and not depending on the host. But that is not always possible as
some of the endpoint designs do require the endpoint to consume refclk from
the host (as I was told by the Qcom engineers).

Thus, fix this crash by moving the controller cleanups to the start of
the qcom_pcie_perst_deassert() function. qcom_pcie_perst_deassert() is
called whenever the host has deasserted PERST# and it is guaranteed that
the refclk would be active at this point. So at the start of this function
(after enabling resources), the controller cleanup can be performed. Once
finished, rest of the code execution for PERST# deassert can continue as
usual.