tools/testing/cxl: Add DC Regions to mock mem data

cxl_test provides a good way to ensure quick smoke and regression
testing.  The complexity of Dynamic Capacity (DC) extent processing as
well as the complexity of the new sparse DAX regions can mostly be
tested through cxl_test.  This includes management of sparse regions and
DAX devices on those regions; the management of extent device lifetimes;
and the processing of DCD events.

The only missing functionality from this test is actual interrupt
processing.

Mock memory devices can easily mock DC information and manage fake
extent data.

Define mock_dc_partition information within the mock memory data.  Add
sysfs entries on the mock device to inject and delete extents.

The inject format is <start>:<length>:<tag>:<more_flag>
The delete format is <start>:<length>

Directly call the event irq callback to simulate irqs to process the
test extents.

Add DC mailbox commands to the CEL and implement those commands.

Reviewed-by: Jonathan Cameron <[email protected]>
Reviewed-by: Dave Jiang <[email protected]>
Signed-off-by: Ira Weiny <[email protected]>

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Changes:
[iweiny: rebase]
[djbw: s/region/partition/]
[iweiny: s/tag/uuid/]

Author: weiny2