PCI: cadence: Use bitfield for *quirk_retrain_flag* instead of bool

PCI: cadence: Use bitfield for *quirk_retrain_flag* instead of bool

No functional change. As we are intending to add additional 1-bit
members in struct j721e_pcie_data/struct cdns_pcie_rc, use bitfields
instead of bool since it takes less space. As discussed in [1],
the preference is to use bitfileds instead of bool inside structures.

[1] -> https://lore.kernel.org/linux-fsdevel/CA+55aFzKQ6Pj18TB8p4Yr0M4t+S+BsiHH=BJNmn=76-NcjTj-g@mail.gmail.com/

Suggested-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://lore.kernel.org/r/20210811123336.31357-2-kishon@ti.com
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>