PCI: dwc: Disable BARs in common code instead of in each glue driver

The current EPC core design relies on an EPC driver disabling all BARs by
default. An EPF driver will then enable the BARs that it wants to enabled.

This design is there because there is no epc->ops->disable_bar().
(There is a epc->ops->clear_bar(), but that is only to disable a BAR that
has been enabled using epc->ops->set_bar() first.)

By default, an EPF driver will not be able to get/enable BARs that are
marked as BAR_RESERVED or BAR_DISABLED (see pci_epc_get_next_free_bar()).

Since the current EPC code design requires an EPC driver to disable all
BARs by default, move this to DWC common code from each glue driver.

BAR_RESERVED BARs are not disabled by default because these BARs are
hardware backed, and should only be disabled explicitly by an EPF driver
if absolutely necessary for the EPF driver to function correctly.
(This is similar to how e.g. NVMe may have vendor specific BARs outside of
the mandatory BAR0 which contains the NVMe registers.)

Note that there is currently no EPC operation to disable a BAR that has not
first been programmed using pci_epc_set_bar(). If an EPF driver ever wants
to disable a BAR marked as BAR_RESERVED, a disable_bar() operation would
have to be added first.

No functional changes intended.

Signed-off-by: Niklas Cassel <cassel@kernel.org>
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Tested-by: Manikanta Maddireddy <mmaddireddy@nvidia.com>
Tested-by: Koichiro Den <den@valinux.co.jp>
Reviewed-by: Manikanta Maddireddy <mmaddireddy@nvidia.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://patch.msgid.link/20260312130229.2282001-19-cassel@kernel.org

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