arc: hsdk_defconfig: Enable CONFIG_BLK_DEV_RAM

We have now a HSDK device in our kernelci lab, but kernel builded via
the hsdk_defconfig lacks ramfs supports, so it cannot boot kernelci jobs
yet.

So this patch enable CONFIG_BLK_DEV_RAM in hsdk_defconfig.

Signed-off-by: Corentin Labbe <clabbe@baylibre.com>
Acked-by: Alexey Brodkin <abrodkin@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>