debugfs: add SMC channel

Provide an SMC interface to the 9p filesystem. This permits
accessing firmware drivers through a common interface, using
standardized read/write/control operations.

Signed-off-by: Ambroise Vincent <ambroise.vincent@arm.com>
Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
Change-Id: I9314662314bb060f6bc02714476574da158b2a7d
12 files changed