sh: sh4a: Bring back tmu3_device early device

Commit 1399c195 ("sh: Switch to new style TMU device") converted
tmu3_device platform device to new style of platform data but removed it
from sh7786_early_devices array effectively removing last three timers
and causing a warning:

    arch/sh/kernel/cpu/sh4a/setup-sh7786.c:243:31:
        warning: ‘tmu3_device’ defined but not used [-Wunused-variable]

Fixes: 1399c195 ("sh: Switch to new style TMU device")
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Rich Felker <dalias@libc.org>