riscv: dts: canaan: fix the k210's memory node

The k210 U-Boot port has been using the clocks defined in the
devicetree to bring up the board's SRAM, but this violates the
dt-schema. As such, move the clocks to a dedicated node with
the same compatible string. The regs property does not fit in
either node, so is replaced by comments.

Tested-by: Niklas Cassel <niklas.cassel@wdc.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20220705215213.1802496-6-mail@conchuod.ie


Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>