riscv: dts: unleashed: Add gpio card detect to mmc-spi-slot

riscv: dts: unleashed: Add gpio card detect to mmc-spi-slot

Per HiFive Unleashed schematics, the card detect signal of the
micro SD card is connected to gpio pin #11, which should be
reflected in the DT via the <gpios> property, as described in
Documentation/devicetree/bindings/mmc/mmc-spi-slot.txt.

[1] https://sifive.cdn.prismic.io/sifive/c52a8e32-05ce-4aaf-95c8-7bf8453f8698_hifive-unleashed-a00-schematics-1.pdf

Signed-off-by: Bin Meng <bin.meng@windriver.com>
Fixes: d573b5558abb ("riscv: dts: add initial board data for the SiFive HiFive Unmatched")
Cc: stable@vger.kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>