dt-bindings: timer: renesas,rz-mtu3: Improve documentation

dt-bindings: timer: renesas,rz-mtu3: Improve documentation

Fix the documentation issues pointed by Pavel while backporting
it to 6.1.y-cip.
 - Replace '32- bit'->'32-bit'
 - Consistently remove '.' at the end of line for the specifications
 - Replace '          (excluding MTU8)'-> '(excluding MTU8)'

Reported-by: Pavel Machek <pavel@denx.de>
Closes: https://lore.kernel.org/all/ZH79%2FUjgYg+0Ruiu@duo.ucw.cz
Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20230727081848.100834-3-biju.das.jz@bp.renesas.com