clocksource: sh_cmt: Add support for multiple channels per device

clocksource: sh_cmt: Add support for multiple channels per device

CMT hardware devices can support multiple channels, with global
registers and per-channel registers. The sh_cmt driver currently models
the hardware with one Linux device per channel. This model makes it
difficult to handle global registers in a clean way.

Add support for a new model that uses one Linux device per timer with
multiple channels per device. This requires changes to platform data,
add new channel configuration fields.

Support for the legacy model is kept and will be removed after all
platforms switch to the new model.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
(cherry picked from commit 81b3b2711072b6047d5f332cd8751a1c5c9a3fb2)
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>