dmaengine: qcom_hidma: implement lower level hardware interface

This patch implements the hardware hooks for the HIDMA channel driver.

The main functions of interest are:
- hidma_ll_init
- hidma_ll_request
- hidma_ll_queue_request
- hidma_ll_hw_start

OS layer calls the hidma_ll_init function during probe to set up the
hardware. At this moment, the number of supported descriptors are also
given. On each request, a descriptor is allocated from the free pool and
filled in with the transfer parameters. Multiple requests can be queued
into the hardware via the OS interface. When client is ready for requests
to be executed, start method is called.

Completions are delivered via callbacks via tasklet.

Signed-off-by: Sinan Kaya <okaya@codeaurora.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>