regions_mm: Fix vhm allocator behavior on memory freeing

[softwarecki]

Platforms based on xtensa have a non-coherent cache between cores. Before releasing a memory block, it is necessary to invalidate the cache. This memory block can be allocated by another core and performing cache writeback by the previous owner will destroy current content of the main memory.

Invalidate cache when freeing allocated memory block.

The memory block allocated by the allocator may be larger than a requested one. If the allocated block size exceeds the memory page size, only enough pages are mapped to satisfy the request. Thanks to this optimization, it don't map memory pages that will not be used. When freeing memory, the allocator knows only size of the allocated block. Information about the
number of pages actually mapped isn't stored anywhere.

Before unmapping memory, determine the number of mapped pages to avoid error when trying to unmap unmapped memory.

[lgirdwood]

@softwarecki LGTM (just have an open on naming) , btw do we need to perform any cache operation on the heap region metadata after the free() ?
@andyross pls review.

[softwarecki]

@lgirdwood:

cache operation on the heap region metadata

Metadata is stored in a separate location, not in a unallocated memory.
But it is a very good point!!! I'm afraid all book keeping should be placed in non-cacheable memory or use cache invalidate/flush... It smells like a more changes is coming...

[tmleman]

LGTM, I would only consider whether it's worth using the CONFIG_INCOHERENT config here.

[kv2019i]

Ready to go when CI passes, @softwarecki can you check the Intel internal CI fail?

[softwarecki]

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