riscv: dts: add resets property for uart node

Add resets property for uart0 for completeness, although it is
deasserted by default.

Signed-off-by: Chen Wang <unicorn_wang@outlook.com>
Reviewed-by: Inochi Amaoto <inochiama@outlook.com>
Link: https://lore.kernel.org/r/807f75e433a0f900da40ebb6a448349c98580072.1706577450.git.unicorn_wang@outlook.com


Signed-off-by: Inochi Amaoto <inochiama@outlook.com>