clocksource: sh_mtu2: Add support for multiple channels per device

clocksource: sh_mtu2: Add support for multiple channels per device

MTU2 hardware devices can support multiple channels, with global
registers and per-channel registers. The sh_mtu2 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>
Tested-by: Wolfram Sang <wsa@sang-engineering.com>
(cherry picked from commit faf3f4f8c805f5f8a786ba544c94bf3e01838388)
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>