pci: add capability helpers

Add a way to iterate over all capabilities in a config space. Add a search
function for getting a specific capability.

Reviewed-by: Punit Agrawal <punit.agrawal@arm.com>
Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
2 files changed