chore(io): remove io_dummy driver

In accordance with [1], delete the io_dummy driver code in preparation
for the v2.9 release.

[1] https://trustedfirmware-a.readthedocs.io/en/latest/about/release-information.html

Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>
Change-Id: If80573d6f889624ef06b099fd267ee85f3a6331e
4 files changed