riscv: dts: sifive: Group tuples in register properties

To improve human readability and enable automatic validation, the tuples
in "reg" properties containing register blocks should be grouped using
angle brackets.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>