media: add SECO cec driver

This patch adds support to the CEC device implemented with a STM32
microcontroller in X86 SECO Boards, including UDOO X86.

The communication is achieved via Braswell integrated SMBus
(i2c-i801). The driver use direct access to the PCI addresses, due to
the limitations of the specific driver in presence of ACPI calls.

The basic functionalities are tested with success with cec-ctl and
cec-compliance.

Inspired by cros-ec-cec implementation, attaches to i915 driver
cec-notifier.

Signed-off-by: Ettore Chimenti <ek5.chimenti@gmail.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
Signed-off-by: Hans Verkuil <hansverk@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>