habanalabs: refactor mmu va_range db structure

Use an array of va_ranges instead of keeping each va_range separately,
we do this for better readability and in order to support access to
a specific range in a much elegant manner.

Signed-off-by: Ofir Bitton <obitton@habana.ai>
Reviewed-by: Oded Gabbay <ogabbay@kernel.org>
Signed-off-by: Oded Gabbay <ogabbay@kernel.org>