handle sof_ipc_host_buffer with non-0 offset #544

On SKL- platforms, we are using sof_ipc_host_buffer for host buffer definition:
/* stream ring info */
struct sof_ipc_host_buffer {
uint32_t phy_addr;
uint32_t pages;
uint32_t size;
uint32_t offset;
} attribute((packed));

Here, the offset is created aimed to make the DMA start copying from/to non-0 offset of the buffer.
Previously, we all set offset=0 in host side, but now we are running into non-0 offset requirement support for runtime suspend/resume cases where we may requirement the DMA resume copying from the previous offset(suspend point), so, we have requirement on FW capability to handle this non-0 offset now.

The basic thinking is that to add this handling into ipc_parse_page_descriptors(), for non-0 offset, we need to organize elem_array[] like this:

offset_page = offset / page_size;
page_offset = offset % page_size;

elem_array[0].dest = page[offset_page] + page_offset;
elem_array[0].size = page_size - page_offset;

elem_array[1].dest = page[offset_page + 1];
elem_array[1].size = page_size;
...
elem_array[m].dest = page[pages - 1];
elem_array[m].size = page_size;

elem_array[m+1].dest = page[0];
elem_array[m+1].size = page_size;
...

elem_array[m+n].dest = page[n-1];
elem_array[m+n].size = page_size;
...
elem_array[pages-1].dest = page[offset_page - 1];
elem_array[pages-1].size = page_size;

elem_array[pages].dest = page[offset_page];
elem_array[pages].size = page_offset ;

with the elem_array[] set correctly, we should be able to handle these non-0 offset cases, these are useful for e.g. DMA trace resume, stream playback/capture resume.