cxl: Add functions to get an instance of / count regblocks of a given type

cxl: Add functions to get an instance of / count regblocks of a given type

Until the recently release CXL 3.0 specification, there
was only ever one instance of any given register block pointed
to by the Register Block Locator DVSEC. Now, the specification allows
for multiple CXL PMU instances, each with their own register block.

To enable this add cxl_find_regblock_instance() that takes an index
parameter and use that to implement cxl_count_regblock() and
cxl_find_regblock().

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/20230526095824.16336-3-Jonathan.Cameron@huawei.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>