drm: atmel-hlcdc: fix layer disable

destroy the pending request

Signed-off-by: Boris BREZILLON <boris.brezillon@free-electrons.com>
drm: atmel-hlcdc: simplify locking architecture

Signed-off-by: Boris BREZILLON <boris.brezillon@free-electrons.com>
drm: atmel-hlcdc: rework layer code

Signed-off-by: Boris BREZILLON <boris.brezillon@free-electrons.com>