clocksource/drivers/sh_cmt: Document "cmt-48" as deprecated

Update the CMT driver to mark "renesas,cmt-48" as deprecated.

Instead of documenting a theoretical hardware device based on current software
support level, define DT bindings top-down based on available data sheet
information and make use of part numbers in the DT compat string.

In case of the only in-tree users r8a7740 and sh73a0 the compat strings
"renesas,r8a7740-cmt1" and "renesas,sh73a0-cmt1" may be used instead.

Signed-off-by: Magnus Damm <damm+renesas@opensource.se>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>