Make epc->ops->clear_bar()/pci_epc_clear_bar() take struct *epf_bar.

This is needed so that epc->ops->clear_bar() can clear the BAR pair,
if the BAR is 64-bits wide.

This also makes it possible for pci_epc_clear_bar() to sanity check
the flags.
Signed-off-by: Niklas Cassel <niklas.cassel@axis.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Gustavo Pimentel <gustavo.pimentel@synopsys.com>