habanalabs: add device memory scrub ability through debugfs

Add the ability to scrub the device memory with a given value.
Add file 'dram_mem_scrub_val' to set the value
and a file 'dram_mem_scrub' to scrub the dram.

This is very important to help during automated tests, when you want
the CI system to randomize the memory before training certain
DL topologies.

Signed-off-by: Dafna Hirschfeld <dhirschfeld@habana.ai>
Reviewed-by: Oded Gabbay <ogabbay@kernel.org>
Signed-off-by: Oded Gabbay <ogabbay@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>