riscv: dts: starfive: visionfive 2: add "disable-wp" for tfcard

No physical write-protect line is present, so setting "disable-wp".

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Reviewed-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>