debugfs: add FIP device

Add a FIP driver hooked to debugfs 9p interface. This is an
abstraction of the FIP filesystem layer on top of a mass storage,
or memory block driver.

Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
Change-Id: If275ea0824763de43ab666dab2a06de5352ff940
4 files changed