accel/habanalabs: improvements to FW ver extraction

1. Rename the func to hl_get_preboot_major_minor because we also set
   the extracted values in hdev fields.

2. Free the allocated string in the calling function which makes more
   sense

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